They put it at ~/go because that's what every official document used as the example $GOPATH, before it had a default value, so it's largely just to minimize change from what they previously recommended.
That said, for something like source code, it makes sense to go into $HOME, so I don't understand this particular complaint the other poster made.
Other people's code shouldn't be in my $HOME if I didn't put it there explicitly. If it's part of the dependencies of a project, it should be either in a cache directory of that particular project, or in the cache directory of the build tool (that preferably conforms to XDG), like all sane build tools do. GOPATH is an incomplete (thus incorrect) solution to a problem that was being solved correctly and completely in other languages (like Ruby).
It's weird that the Go developers were working in such isolation that they didn't pick up on this. All programming languages that I know of that work on modern tooling (Haskell, Rust, Node.JS, even C#!) adopted the Ruby style dependency management when it turned out to be correct years ago.
In my comment I say that it's better than the way Go did it, and Go is switching to the Ruby style, so maybe you could add some kind of argument why it's actually not better than that in any other language?
I can't remember the last time I had a version management problem in Ruby, though the ecosystem is so stable right now not many backwards incompatible things happen any more.
That said, for something like source code, it makes sense to go into $HOME, so I don't understand this particular complaint the other poster made.