This is inherent to the domain of systems programming. One-size-fits-all solutions only suffice until you need extreme performance. So, for example, Rust provides a basic hashmap in the stdlib, and as a generalist hashmap it's quite close to state-of-the-art. But as a generalist hashmap it's also beaten in specific applications by specialist datastructures, and Rust needs to provide support for building those specialist datastructures in a way that makes them feel just as first-class as what the stdlib provides.

Go gets away with what it does because it's for domains where it's acceptable to trade uniformity for performance. This is not a bad thing! Go is quite performant. But Rust ultimately isn't competing with Go, it's competing with C.

And note that I say all this as someone who is, in fact, a stdlib maximalist. But I also say all this as someone who is conscientious and informed of the realities of what it takes to design and maintain a secure, high-performance stdlib.