Why? Can't the linker or post-link optimizer reduce all near calls, leaving the more complicated mov with immediate form only where required?

Once the compiler has generated a 32-bit relative jump with an R_X86_64_PLT32 relocation, it’s too late. (A bit surprising for it to be a PLT relocation, but it does make some sense upon reflection, and the linker turns it into a direct call if you’re statically linking.) I think only RISC-V was brave enough to allow potentially size-changing linker relaxation, and incidentally they screwed it up (the bug tracker says “too late to change”, which brings me great sadness given we’re talking about a new platform).

On x86-64 it would probably be easier to point the relative call to a synthesized trampoline that does a 64-bit one, but it seems nobody has bothered thus far. You have to admit that sounds pretty painful.