I think you vastly underestimate how many edgecases there actually are. Every one edge case might be a small userbase, but combined, all those small userbases make a significant userbase for whom Linux is less than ideal. And (just a hunch) on Lemmy, this % of users is actually larger than the population at large. Tech-savy people tend to use more obscure programs.
Some edgecases I happen to know(because I happen to fall into three edgecase groups!)
VR
adobe stuff
Many music plugins
Those are two creative edgecases. And I believe using your PC for creative work is actually quite a significant userbase.
And sometimes even IF a product is supposedly supported on Linux, it doesn't work straight up. I recently tried to install Ubiquity's Unify program on my Pop!OS, but nope, errors before even installing. Happened to need all kinds of weird dependencies that are outdated and are hard to install. Even when following Ubiquity's install guide. On windows it just worked. Another edgecase, but it adds up.
So I disagree on your "majority" statement. Especially on Lemmy, I don't believe that to be true at all.