The Go team has, until recently, been quite open about not being confident enough in their own abilities to implement it well in Go. Maybe to the point of absurdity, but they were explicitly warned by designers of other popular languages (specifically some of those on your list, I believe) to not be cavalier in how they add generics.
That doesn't mean nobody on earth can implement generics well. I'm sure if someone from the C#, Java, Scala, etc. teams, with the necessary expertise, wanted to step in and contribute generics for Go, it would have been a welcome addition. At very least for the community who would have jumped all over a fork with generics. However, I do not see that code anywhere. You cannot force people to do things they do not willingly want to do.
Now that the Go team has had enough time to put for the effort to learn more about generics and the research related to them, they feel more confident about being able to add them in a somewhat reasonable way and have officially announced that they will be added in the near-ish future.
The Go team has, until recently, been quite open about not being confident enough in their own abilities to implement it well in Go. Maybe to the point of absurdity, but they were explicitly warned by designers of other popular languages (specifically some of those on your list, I believe) to not be cavalier in how they add generics.
That doesn't mean nobody on earth can implement generics well. I'm sure if someone from the C#, Java, Scala, etc. teams, with the necessary expertise, wanted to step in and contribute generics for Go, it would have been a welcome addition. At very least for the community who would have jumped all over a fork with generics. However, I do not see that code anywhere. You cannot force people to do things they do not willingly want to do.
Now that the Go team has had enough time to put for the effort to learn more about generics and the research related to them, they feel more confident about being able to add them in a somewhat reasonable way and have officially announced that they will be added in the near-ish future.