Suppose I want my project to have as many contributors as possible. Generally do you think more people are inclined to contribute (upstream) if the code is permissive or copyleft or do you think it doesn’t really matter?
I am happier when I see copyleft but let’s be honest, I would contribute to an interesting, useful project regardless of their choice between MIT and GPL. Same for companies: some prefer MIT, but there is no way they are not going to contribute to the Linux Kernel just because of copyleft. So bottom line is: make something that people enjoy/find useful and see contributors flocking.
CLAs are a different matter: I do not contribute to projects which ask you to assign them copyright unless I 100% trust the organisation behind them.
What does CLA mean?
GPL is the only good license out there. MIT just leaves too many opportunities for abuse because corporations won’t ever do what is in the best interest of humanity.
GPL with a paid commercial option for companies that need closed source derivatives.