I find that this is something reflective of most modern language ecosystems, not just Rust. I actually first started noticing the pervasiveness of MIT on npm.

For me, I am of two minds. On one hand, the fact that billion-dollar empires are built on top of what is essentially unpaid volunteer work does rankle and makes me much more appreciative of copyleft.

On the other hand, most of my hobbyist programming work has continued to be released under some form of permissive license, and this is more of a reality of the fact that I work in ecosystems where use of the GPL isn't merely inconvenient, but legally impossible, and the pragmatism of permissive licenses win out.

I do wish that weak copyleft like the Mozilla Public License had caught on as a sort of middle ground, but it seems like those licenses are rare enough to where their use would invite as much scrutiny as the GPL, even if it was technically allowed. Perhaps the FSF could have advocated more strongly for weak copyleft in area where GPL was legally barred, but I suppose they were too busy not closing the network hole in the GPLv3 to bother.

I love the MPL and I use it wherever I get the opportunity. IMO it has all the advantages of the GPL and lacks the disadvantages (the viral part) that makes the GPL so difficult to use.