Also, 64-bit code and especially data are just larger, because every address is 8 bytes, and data has to be aligned on at least 4-byte boundary. You can still

Also, 64-bit code and especially data are just larger, because every address is 8 bytes, and data has to be aligned on at least 4-byte boundary. You can still have very tiny Linux with a relatively modern kernel on tiny m0 cores, and there's ELKS for 16-bit cores.