Devil’s Advocate: just because something can be preserved doesn’t mean it’s worth preserving. For all the golden games of the 80s and 90s, there were even more turds, and the same goes for other software.
Really though, the issue comes down to kernel bloat and volunteer support. Imagine having a kernel that’s bigger than Ubuntu, simply because it supports decades of hardware that only a shrinking, tiny minority uses, and an equally shrinking number of people who care to try to patch it so it stays up to date. It’s untenable.