> I don't see why a company that refuses to add to a GPL project has a "decent change" of releasing their code under a more permissive license.

It's simple in my experience.

Many big companies have some set "A" of code that they want to keep private, and some set "B" that they don't care about keeping private.

Lawyers are worried that at some point someone will accidentally include GPL code in something from "A" and force it to be made public. So they ban GPL entirely. They could in theory just ban GPL code from "A" and allow it in "B", but they can't trust that among thousands of employees none will make a mistake, so they just ban the GPL entirely.