You can absolutely keep using older X11 desktops or WMs forever, that doesn’t mean you’re getting the same experience as everyone else on a modern Wayland desktop or WM
The main problem is that nowadays a lot of software is JavaScript downloaded when web browsing. And that might just be too demanding for ancient hardware if it was never tested on it.
The thing about Linux is that you have choice. You can put Xubuntu on a laptop with a Core 2 Duo and 4GB of RAM and it will fly.
You can absolutely keep using older X11 desktops or WMs forever, that doesn’t mean you’re getting the same experience as everyone else on a modern Wayland desktop or WM
There is a world of difference between “not getting the best experience” and “the entire computer is unusable now”.
The main problem is that nowadays a lot of software is JavaScript downloaded when web browsing. And that might just be too demanding for ancient hardware if it was never tested on it.