Another reason is kind of a general thing with programming language design: Go, like Java or C, has relatively few concepts in the language and stdlib. This means you’re relatively quick to have seen all of them.
But this also means that for various tasks, these concepts that were left out, would have been the right tool. For example, Go doesn’t have enums.
Generally, it’s still possible to create all possible programs, because of turing-completeness, but it will be more cumbersome and more boilerplate-heavy.
So, as a rule of thumb, the more concepts are provided by the language and stdlib, the more you have to learn upfront, but the less pain you have long-term.