Rust has no stable inter-module ABI, so everything has to be statically linked together. And because of how "viral" the GPL/LGPL are a single dependency with that license turns the entire project into a GPL licenced one.

So the community mostly picks permissive licenses that don't do that, and that inertia ends up applying to the binaries as well for no real good reason. Especially when there's options like e.g. MPL.