This is talking specifically about Steam, not PC using Epic, GOG, Direct2Drive, etc. PC was my primary system. I'm not sure why you haven't done this, but every PC gamer I knew growing up bought games day one even while we played older games.
And this isn't exclusive to PC either.
On the PS5, I can go back and play terrific games from the 70s and onward. On the Switch, it's the same thing. Etc, so having BC isn't exclusive to PC. I have 100s of physical games on PC I still play sometimes, but I still play new games on PC too.
PC does have generations. It's even in the wording of new CPUs and GPUs. When giant leaps happen on hardware, that's a new generation. You can still use you old hardware to play most games (same with consoles), but there is a leap forward.