Also Copyright is a pretty US thing. Law differs and many Countries don't actually allow it. Also since you brought up Getmany already: https://en.wikipedia.org/wiki/Copyright_law_of_Germany#Trans... Germany is such a country and even if you were to assign copyright to them it would be legally void to the best of my knowledge. And also other countries that base it on moral rights.
Copyright law is very different between countries and way too strong to just transfer for such a use. If they really wanted to, they should have made a license to handle it exactly the way they wanted.
Some other people argue it's not necessary, and while that might be true, it's better to be safe than sorry. Not to mention that all GNU projects are GPLv3-or-later anyway (so any contribution would be able to be upgraded anyway since it's licensed in such a way that you can use it under GPLv4). If you refuse and license your change under GPLv3, it won't get merged.
Really, FSF copyright is a very good thing, and you can even do it completely digitally in the US and Germany (used to be that you had to use snail mail to receive forms and send them back). People shouldn't get scared away from contributing to GNU projects that choose copyright assignment. There's no better place to protect the GPL than at the FSF.