Well, there are some (good) reasons. From different perspectives:

• sometimes you’ll end up at your own restrictions from “back then”. Where you can’t fix or add anything but need to rebuild the foundation.

• a simple monetary reason. Just giving updates for free to people who bought a license 15yrs ago, is not a sustainable business-model.

• technological advancements you couldn’t predict. Like TPM and whatnot.

• simple marketing for clueless people. “I’ll better get the newest macos, windows still is at winXP” or the likes.

I’m not fan of it either. Win10->win11 wasn’t much of a change. Except things most people don’t care about (but need more modern hardware for) and the horribly nasty startmenu. For gamers there are some nice things, but those could’ve been a patch, like you say.