You know how SSDs wear out right? Well, the transistors in a processor can wear out over time too. Granted, things in processors work very differently than in SSDs, but semiconductors are still semiconductors, and they degrade over time. Also, connections, solder, thermal damage (even at standard operating temperature the processor is taking some amount of damage from releasing heat) and many other things will wear over time from consistent use.
It’s a bit difficult to imagine because the wear is so different from what we’re used to seeing, but it still happens in processors.
Apple is the only desktop OS company I know of that doesn’t make x32 operating systems anymore (as far as I know, Darwin may still have x32). Windows cares a lot about backwards compatibility with hardware, as does linux developers, so they keep the x32 version around for those still running on old hardware.