It’s not that fantastic for low level systems programming due to garbage collection and the runtime. If you’re working with C et al, you’re generally doing something that requires extreme control, and Go is too high level to do that nicely - you can use it of course, but it’s just... weird.

C++ is not really a low level systems language because, very broadly speaking, low level stuff doesn’t benefit as much from the extreme flexibility and abstraction capabilities of C++. It’s used more as a high-performance application programming language for large, complex stuff. Go doesn’t fit that niche because it’s just not a very powerful language.

The niche where a simple language like Go is applicable for systems stuff without being too slow or high-level is extremely small. It’s a fantastic language for working on business-logic type stuff, web backends, etc, and excels when working with less experienced developers or larger teams. It’s as easy as python et al but actually has reasonable performance. But it’s not really a systems language for serious systems stuff.

Automatic heap allocation and garbage collection are big ones. People debate this endlessly, and it's true that undeniably-systems-ish software projects like Docker and CockroachDB are written in Go. But at the end of the day there will always be some systems that cannot be written in Go because of how it manages memory, which is not the case with C, C++, or Rust.

Go is not systems programming language because it has mandatory garbage collector.