The Go developers, many years before implementing generics, made it clear they were open to the idea. It was more about how it would fit into the language and them agreeing on it.
To their credit, they don't just throw things into the language because it's trendy or "cool" at the moment. Even if people disagree with their decisions, they are well considered and thought about decisions.
It’s funny you call out Java, when it is exactly the language famous for taking advantage of being the last mover — even its original intros mentioned it!
Also, languages don’t start in a vacuum, they shouldn’t have to go through the whole process from zero each time — Go absolutely failed by not incorporating it from the first version.
https://news.ycombinator.com/item?id=9622417
> We have spoken to a few true experts in Java generics and each of them has said roughly the same thing: be very careful, it's not as easy as it looks, and you're stuck with all the mistakes you make.
The Go team does their homework, and they do it thoroughly. I respect that more than anything about the language. Compare with Java, that had been stagnant in committees for nearly a decade, or with Javascript, that has been bolting on features left and right; I'm mainly thinking of the half-baked OOP addition.