It’s a play on “permissive” license.

A derogatory term for copyfree licenses

Permissive license + complaining when companies don't contribute back from their forks.

I've worked on plenty of BSD and MIT licensed code. I've never complained about lack of contribution. You're projecting. Please stop.

I'm not the person who used the term "pushover license". I just explained why some people use the term.

Do rust projects have a reputation for complaining about corporate forks not contributing back code?

Not in particular, but it's pretty common for permissively licensed projects to complain about companies complying with their license instead of what they imagine the license to be, then relicensing to a proprietary or copyleft license (e.g. Elasticsearch for a high-profile case but there are many others). This lead to some people disliking permissive licenses.

Personally I dislike them because they don't preserve end-user freedom, I prefer the MPL. But if someone wants to donate their work to for-profit companies that's their choice.

'Pushover licence' is a licence which may grant freedom, but doesn't care to protect it. One may modify software under a pushover licence and release their modifications as non-free software. Another, more common name is 'permissive licence'.