The Go standard library uses ~/Library/Application Support as well [1]. Given the Unix credentials of Golang's top folks, I would assume there's a good argument in favor of this decision?
On the other hand, you can be more flexible and allow the user to pick how these are determined, as the Rust crate etcetera[1] does. This gives you the best of both worlds.
[1] https://docs.rs/etcetera/latest/etcetera/app_strategy/index....
$ ls -ld ~/go
ls: /Users/mdaniel/go: No such file or directory
$ go install -v "github.com/jmespath/go-jmespath@latest"
go: downloading github.com/jmespath/go-jmespath v0.4.0
package github.com/jmespath/go-jmespath is not a main package
$ ls ~/go
pkg/
$ rm -rf ~/go
rm: /Users/mdaniel/go/pkg/mod/github.com/jmespath/go-jmespath@v0.4.0/.travis.yml: Permission denied
$ rm -rf ~/go 2>&1|grep "Permission denied" | wc -l
686From my perspective it makes sense as a default for go, which may be used to make either apps (things with bundle identifiers that go in /Applications) or CLI applications (which I wish would use ~/.config, but I understand that that's just my preference)
POSIX exists, because out of UNIX System V, every clone went down their own merry way.