Compilation can be very intensive, and it's detrimental to a developer's workflow if they must wait for long recompiles.

Rust was originally written in OCaml before being self-hosted, and it wouldn't be as fast (or would be even slower ;) ) today if it was still OCaml.

And remember, low-level =/= poor abstractions. I think there are several novel abstractions available in Zig which the compiler devs probably want to make use of themselves.