Put Rust and Go in front of a python coder who wrote dozens of web services using flask - and I am pretty sure I can predict what tool he'll pick. Sure you could write web services in Rust, that's not what I'm arguing, learning Rust for writing stuff like that is simply not worth it for people having to write such services.
Rust's complexity is comparable with C++, and the main reason for this complexity is to address problems that are mainly seen in C/C++ applications. Rust's reason for existing is simple: modern low-level language with built-in (memory) safety with no performance trade-offs (implying concurrency support etc). That makes it squarely aimed at C++, where developers accept the complexity as a trade-off for performance.
Go's reason of existence and goals are completely different, it addresses the gap that existed between compiled and interpreted languages. It wants to be a simple, safe, easy to deploy language that offers more performance over classic scripting languages and thus is able to address more performance-critical issues. It's main target is clear: servers and networking services, where a GC's impact less important due to the I/O bottlenecks in most scenario's.