The reason why most drivers are more readily available in 9.5 & 10.5 lofts is simply because that's what people buy. Whether or not that's the proper loft for most people is totally irrelevant, because they're going to make what sells the best not what they feel most people should play with. As @Rickochet mentioned, with the decline of the industry companies have begun trimming fat, and the things that get trimmed are those that don't sell well - regardless of how important they may be to some people.
One of the most frustrating things I run into as a fitter is trying to convince people that they need a higher lofted driver. I deal with a lot of senior golfers in the winter during "snowbird" season, and so many of them think they need a 9.5 or 10.5 because they think the ball is going to roll forever which is going to give them more distance. Yeah, sure it'll roll forever, but your carry distance is going to be 30% less than a higher loft and your overall distance probably 10-15% less. And what happens if you need to carry a bunker/hazard off the tee? Or what if you play early in the morning when the grass is still wet which kills your rollout distance? People are just so convinced that 9.5-10.5 drivers are what everyone should be using, that even when I show them on my simulator that they carry a 12 or 14 degree driver farther and it goes farther overall, it's still nearly IMPOSSIBLE to get them to actually commit to buying it. It's ridiculous. I would love it if I could have a company make be a bunch of 12-14 degree drivers with 10.5 stamped on the bottom of them!! 😂😂
So anyway, back to your original question - companies make whatever sells. And if 9.5-10.5 drivers make up 90% of your sales, then it may not make financial sense to even manufacture/stock them in 12, 13 or 14 degrees. Maybe they'll offer the higher lofts in one or two heads, and then those few who do want a higher loft will just end up buying one of those models.