Opensource

This is not a rust thing. Most popular languages with a library distribution system favour permissive licence like MIT Apache 2.0 or BSD or similar.

More mainstream languages are that way because cooperations use them - most people learn a d use the language that will get them a job or the ones used by where they work. And if the language it tooling and libraries where not permissive they would likely not be allowed to be used in a lot of companies.

And most of the libraries written for languages these days are done by people paid to do it, either directly by being hired or sponsored to do so or so they can be used when they are at work. The GPL would basically not allow the vast number of people who are writing code from using the library.