Thing is, as soon as you provide users with one more feature, some of these users want even more features: "yeah, enums are great, but I would like to have type safety with them; oh, type safety is important, but why not have sum types, after all? Oh, now that we have sum types, why not add pattern-matching?"

All of these features are great, but they make the language harder to master, and tooling harder to write. This is a tradeoff, there are many languages that implement all the features its users want (I can think of C++, Rust, probably C# too), why not let other language designers try another way?

I have to admit I wouldn't dislike an enum construct in Go, just syntactic sugar that would be equivalent to the type foo int + const block, but I certainly won't push for it.