Even with all the Rustaceans rewriting in Rust while abandoning the GPL, their flagship - Servo - is GPL licensed.
There is an aversion to CLAs among those donating their time, and with that an aversion to permissive licenses.
Im sure both will be around for a long time, but in the very long term GPL wins.
And even even that's a bit of a problem for the Servo project, as it makes it hard to move code between Servo crates and other Rust ecosystem crates (which are typically MIT/Apache2.0), which means that Servo is it's own "island" somewhat disconnected from the rest of the Rust ecosystem.
(there's nothing inherently wrong with the MPL, but it being a different and incompatible license to the rest of the ecosystem does cause problems)
Clang/LLVM: permissive
Rustc: permissive
Firefox: MPL
Chromium: permissive
Postgres: permissive
LibreOffice: MPL
CPython: permissive
and so on...