Supporting 32bit is not 'simple' and the difference between 32bit hardware and 64bit hardware is not big.

The industry has a lot of experience doing so.

In parallel, the old hardware is still supported, just not by the newest Linux Kernel. Which should be fine anyway because either you are not changing anything on that system anyway or you have your whole tool stack available to just patch it yourself.

But the benefit would be a easier and smaller linux kernel which would probably benefit a lot more people.

Also if our society is no longer able to produce chips in a commercial way and we loose all the experience people have, we are probably having a lot bigger issues as a whole society.

But I don't want to deny that it would be nice to have the simplest way of making a small microcontroller yourself (doesn't has to be fast or super easy just doable) would be very cool and could already solve a lot of issues if we would need to restart society from wikipedia.