Rust is doing a lot more under the hood. C doesn't track variable lifetimes, ownership, types, generics, handle dependency management, or handle compile-time execution (beyond the limited language that is the pre-compiler). The rust compiler also makes intelligent (scary intelligent!) suggestions when you've made a mistake: it needs a lot of context to be able to do that.

The rust compiler is actually pretty fast for all the work it's doing. It's just an absolutely insane amount of additional work. You shouldn't expect it to compile as fast as C.