[cat199]

This presumes that:

a) generic programming is a new thing

b) any of those people you mention aren't using go for some things and other things where this feature is desired

c) that the feature will 'at best' be at level X

d) that level X won't be enough to satisfy some use cases

and a whole host of other things, not least of which the fact that go itself was invented to suit some purpose after other languages existed, and has been successful for many users