Title is slightly misleading, it is not leaving behind 486 types of CPUs individually, but the "486 CPU".
Can most software even compile for 486? I don't think there's anybody out there testing their software for that target.
Good.
Removing tech debt is important
There is always netbsd, which prioritizes portability.
Whether you like it or not, linux is a commercial operating system primarily designed and built by people working for commercial entities, to solve commercial problems.
Nobody in the commercial world is running 486, and supporting old CPUs makes it harder to maintain and build features for modern hardware that commercial entities use.