Doc is intentionally very restricted in what it prints, to keep SNR high. The goal is explicitly to not start printing anything that might be useful, like godoc does.

It's possible that if there are no Go source files in a directory, we could list the subdirectories, but I don't even think that's right: then we'd have to decide whether to print them when there is a valid package that also has subdirectories, and I think the answer that must be no. If you say 'go doc math' you are not (usually) asking about math/rand.

In this case, there is already a command for listing packages: go list, as in go list ./....