Comment by Joker_vD

> would make... data structures bigger for "no reason"

This was the main reason that in stayed 32 bits. Not because larger footprint of structs would be catastrophic — it wouldn't: the 64-bit migration was motivated mainly by the fact that the 32-bit architectures couldn't easily address all that actually existing physical memory past 4 GiB (and virtual memory as well) — but because lots and I mean lots of on-disk data structures were defined in terms of char/short/int, people routinely dumped/gulped their data structures as-is, with no marshalling, so changing the size of int would break literally everything that worked with on-disk data, starting with the filesystem implementations themselves.