The thing about simplicity is making the language simpler often makes programs themselves more complex. For example, in a language without generics, if you have 10 different versions of the same function that only differ by a type parameter, you have to either write them 10 times (meaning anyone reading the code has to read 10 different functions), or you have to write some code generator (meaning anyone reading the code has to now understand your code generator). And, all this cost in the complexity of programs is to avoid something that, in my opinion, _barely_ makes the language any more complex.
So you're not uniformly increasing simplicity. I do agree that when there is a way to make a language simpler without any other downsides (e.g. making programs more complex or error-prone), it should always be done!
Most people, even Go programmers, would think it was silly if you couldn't define your own functions and had to copy-paste blocks of code everywhere, so clearly they aren't against abstraction in principle. And I don't think generics is a particularly more complex form of abstraction than the ability to define functions is! The fundamental difference is not the level of abstraction, but just that _it didn't exist in C_, and the version of it in C++ (templates) is extremely difficult and unwieldy. So presumably that's what the designers of Go were afraid of.
> One question I ask in earnest, why do people not just use another language rather than try to get features jammed into Go?
I have to use Go because I am working in an ecosystem that is entirely in Go. Rewriting it in another language would be much more effort than is feasible. When I work on personal projects not for work I don't use Go at all.
Also, not everyone uses Go because it lacks features for abstraction; there are other reasonable reasons to use it, for example if one likes the Goroutine-style concurrency model.