Sorry, but how can you not get this? The smallest subset defines what you can use at least in the core. You have to add workarounds to make it work. Which takes up time of developers and increases the code complexity. Every configuration option increases the test complexity.
Therefore if an architecture is no longer needed then nuke it. What's the point of hanging on to 386? I doubt that any new machines today are shipped with 386 CPUs. Even embedded radiation hardened special systems are now having better CPUs, such as Pentium-compatible or some PPC.
And the systems still running are certainly not upgrading to a new kernel.
Therefore if an architecture is no longer needed then nuke it. What's the point of hanging on to 386? I doubt that any new machines today are shipped with 386 CPUs. Even embedded radiation hardened special systems are now having better CPUs, such as Pentium-compatible or some PPC.
And the systems still running are certainly not upgrading to a new kernel.