It’s not really something developers want to think about very much so they often just use the default.
Do you think it was intentional ideological decision by the Rust developers or some other contributors/interests to make permissive the default? Or a random decision that has ended up being consequential because of the popularity of Rust?
I have noticed for a long time that github promotes MIT license. It lets you use any, of course, but puts a real positive shine on MIT. My perception is that this is a purposeful intervention by MS into FLOSS to promote MIT.