If you are wondering "why drop support for the 386?," the diff for the removal of 386 support from the Linux kernel is a good read:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

tl;dr atomic instructions XADD and CMPXCHG, and serious bugs in many 386 CPUs. Also BSWAP was added in the 486 and speeds some things up a lot.