They compile from source code elegantly, sure. But you don't always have the source code available. Removing implications of the underlying platform makes it easier to change out hardware in the future. It's so that once the next Intel bug comes out, you can just shed Intel CPU's in favor of ARM, RISC-V, or even big-endian POWER.

Go also doesn't cross compile with cgo that elegantly. Having the platform run the output of C compilers means that you can remove that from your runtime assumptions as well.