I am complaining about the language (phrasing) used: a Python, TypeScript or Java program might be truly portable across architectures too.
Since architectures are only brought up in relation to dynamic libraries, it implied it is otherwise as portable as above languages.
With that out of the way, it seems like a small thing for the Go build system if it's already doing cross compilation (and thus has understanding of foreign architectures and executable formats). I am guessing it just hasn't been done and is not a big lift, so perhaps look into it yourself?
they're only portable if you don't count the architecture specific runtime that you need to somehow obtain...
go doesn't require dynamic linking for C, if you can figure out the right C compiler flags you can cross compile statically linked go+c binaries as well.