At the first computer reseller I worked for (16-17 years ago now), a pretty small company with a few huge customers, the owner showed me his $10,000 parts room. It was smaller than my walk-in closet at home (and I have a SMALL house). So $10,000 is a lot of money to a small company, right? For his first few years of business, all of his various customers kept asking him to keep certain parts in stock, to get repairs done more quickly when needed, etc, etc. And in the interest of growing his business and trying to keep his customers happy, he started buying the parts they asked for and keeping extras on hand. Then, slowly but surely, the customer would retire a model of computer or printer or server or accessory, and would no longer need parts for it. But that reseller still had the parts that nobody wanted any more, and pretty soon he had $10,000 worth of parts that he could no longer sell. At which time he cut WAY back on stocking parts. After all, most of the stuff we needed could be overnighted from the manufacturer or some other bigs parts house themselves. Next day isn't bad for most things.
And so my opinion about companies stocking parts has always been tempered by that experience. A car dealer may not be on the same scale as that small company, but I'm sure owners and managers are aware of that kind of situation themselves. Auto parts are expensive as we all know, and take up space. And how many smart's are in a given city to buy such parts from a dealer? Currently, we also all know that number is quite small. At least the local auto parts places are starting to list parts for our cars, that's a change from just months ago. Even if they're special order, that's much better than no availability at all. Just my own ramblings, sorry for droning on.