In Canada we had a national store called 'Danier' which closed down last year. They probably had trouble selling jackets because of two reasons: the designs were surprisingly terrible, and the quality of manufacture was unreliable at best.
In larger cities like Toronto or Montreal you'll find biker stores that deal in leather jackets purpose-built for riding, and you'll also find boutique high-end fashion stores that always have a leather selection. One is for function, the other is for showing off. There are benefits and drawbacks to both, usually in terms of fit, cost, material, finishing, and overall 'look'.
You mention 'wondering why' leather jacket stores are so difficult to find, or perhaps that they are as rare as hen's teeth these days. In my view it's because of a few reasons that all contribute to a rather depressing package:
1) The average person today has less disposable income than they did before. The middle class is disappearing in the western world, which is why the majority of high-end goods bought and sold here are to people from societies that are currently experiencing a financial boom; mainly China and a few Arab nations, to be precise. However 'foreign investors', as the media enjoys labeling them, are unable to sustain an entire industry in a country, which is why you'll find leather jackets in fashion boutiques but you won't find a store or chain devoted solely to this product. Considering that it is nearly impossible to own property without two incomes, and that about 3/4 of the total population is living paycheck to paycheck, the ability to pay $500+ for a single item of clothing is out of reach for an increasing number of people. Disposable income is disappearing.
2) The material is unforgiving. Most people will find it a nuisance to get fitted properly for a suit, but at least they might be convinced of the necessity due to the everyday wear they'll get out of it for their job. To find a motorcycle jacket off-the-rack that fits properly is difficult for most, and to go custom is an extra cost that, once again, many can't afford. It's not like a synthetic jacket that, though ill-fitting, will not be noticeable to anyone. A poorly fitted leather jacket looks like a black plastic bag, and is obvious to the untrained eye. An otherwise fine jacket is made to look bad, and the person wearing it enjoys the same fate. This is all trouble that most people can't be bothered with. To make matters worse, fitting seems to depend heavily on the manufacturer and the customers they perceive as being the most numerous. Wested off-the-rack jackets suffer from a huge midsection/stomach which makes their regular Indy jackets look round, but given their regular clientele, they've made the choice that works best demographically. AllSaints leather jackets seem to go for the narrow-shoulder look that is very common in Britain...not useful at all for anyone who has broad shoulders. Given that the ideal leather jacket is the one that looks like it is a direct extension of your physical proportions, why would anyone today want to bother spending the time and money to find one that fits them like a glove? It's harder than finding a good pair of jeans that fit properly. The difficulty of the material is the problem.
3) Fashion is disposable today. Not that is wasn't decades ago, but we live in a disposable world where technology is outdated every 2 years. Fashion and style are likewise disposable, but instead of having trends that last for say 6 or 7 years (think of the fluorescent colours that dominated the 1980's all the way until 1994) we have trends that last as short as 2 months. The internet has accelerated this, of course, because now fashion has a direct worldwide platform that didn't exist decades ago. The ability to sell people things they don't need is predicated on how easily you can convince them that what they have is obsolete. With technology that's a simple case...computing is always advancing, requiring more powerful hardware to run. But with clothing you need to force an obsolescence in style. This force used to exist in the form of social enforcement; in the most basic of terms, one could be ridiculed for dressing out of style, or even for wearing white after labor day. Today, there is no ridicule because ridicule of any sort against a person has been outlawed. Critique is socially unacceptable today, and thus people happily do whatever they want to do with fashion. In theory, this should lead to more people wearing leather jackets, due to their longevity of usage. But what it in fact leads to is young people buying leather jackets from used clothing stores; go vintage, it looks better, and it costs less. As for the fashion industry, leather jackets also provide a problem. Consider that great leather jackets last a lifetime; this is entirely antithetical to the fashion industry. Why would they shoot themselves in their own foot by trying to sell you something that you'll never need or want to replace? It's like the razor blade industry. You can use a straight razor, get it sharpened once every 6 months, and be happy for the rest of your life...or you can buy the 'new' men's super razor with 6 (!) blades that you throw away in a week or two. It is against the interests of fashion houses to support styles that do not need to change AND that are expensive to produce. It's unnecessary for a young person to buy new, because vintage options are less expensive, 'cooler', and easily discarded when fashions change.
4) The new generation doesn't need them. Consider the average 18-20 year old. They've likely grown up with synthetics materials all their lives, with clothing that is temporary and style that is permanently transformative. Someone gives them an idea; get a great leather jacket. The first thing they'll think of is 'why would I spend the money on this instead of taking the same money and buying a new phone or a new computer?'. You say, 'because it'll keep you warm, it'll protect you, it'll look good on you, and it'll last a lifetime if you take care of it'. They would respond quite easily with something like, 'yeah, but a $20 jacket would keep me warm, I don't need protection from anything, cheaper clothing will look just as good on me, and why would I want to wear something my entire life? That's boring...'. You could try to trick them by saying, 'but tradition...style...exclusivity....', but they would never take the bate. They hate tradition, style must be non-conformative, and they can get their exclusivity from the tattoo they got last week, which incidentally was done in the same exact spot as the ones their circle of friends have. The point is, leather jackets are unnecessary to the young people in the modern world, not only for riding, but also as a status and style symbol. This is why so many upper end elder leather manufacturers are advertising their jackets using words like 'tradition', 'heritage', etc...it's the easiest way to trick people with too much money and not enough knowledge to part with their cash, and they don't care that it's alien to the younger generation because they wouldn't want to wear this stuffy antiquated material anyway.
An industry like this cannot sustain itself the way it could decades ago, and for now it'll be in specialty stores. But that's okay really; I'm the only one of my friends who wears leather exclusively, even in winter...most of them can't be bothered, but it doesn't change the fact that they love how my jackets look on me, and always wistfully think about getting one themselves, one day. There will always be nuts like us on forums like this, discussing the benefits or drawbacks of this leather or that, praising good purchases online and commiserating with those who have purchased a jacket that doesn't quite fit. We'll be there to cheer on a person who tries to pull off a style they've never tried before, and we'll be there to gently critique a member who's not sure if the sleeves are long enough. The world is changing, but that doesn't mean that leather won't make a comeback. It's just a matter of time, in my view, and when it happens, I'll be there.
Nihil tam incertum nec tam inaestimabile est quam animus multitudinis.
- Titus Livius