Linus has explicitly stated he doesn't like GPLv3, and neither do many others - corporate and otherwise - so all a copyright assignment would do is potentially

Linus has explicitly stated he doesn't like GPLv3, and neither do many others - corporate and otherwise - so all a copyright assignment would do is potentially remove their rights to use code they wrote. Either by making it GPL3 and have them lose access to it in their use case, have the code made proprietary so they can't use it at all, or switch to another license entirely (BSD, MIT, or public domain which are all "worse" than GPL per the GPL3 folk). I don't understand people who would assign copyright for OSS code they wrote to someone else, because that's just a giant F U to the entire concept, and has literally no up side for anyone other than the new owner.