I mean, old OS’s are great for running plenty of legacy software like old games. I understand issues with hardware compatibility and stuff, but think about virtual machines. Microsoft could do something like bring back Virtual PC and pre-load Virtual PC with the old OS’s, or give anyone an old Windows ISO upon request as long as they had a legitimate copy of Windows 10. It’s not like they’re profitable, so Microsoft wouldn’t be losing any money doing it. I mean, virtual machines are a thing, so there’d be no need for Microsoft to update them or anything for today’s hardware.
I personally think old Windows versions still have a place in the world, because regardless of how ‘useless’ they are, they’re still good for a little bit more than just nostalgia.