Why would I ever need to sign such s thing? If I contribute to an open source project, isn’t it obvious that I agree to publish my code under whichever license the project is published under?
The entire point is that the project can later change the license even if you don’t agree. Make of that what you want…
A good reason to ask that is to make sure the project licence can be changed in the future, because all copyright is owned by the project, not the contributors. Otherwise you would need to ask permission from all contributors.
Often, the contributor license agreement says that you - the contributor - transfer the copyright of your contribution to the project/company.
This is used to get the community contributing to the project while making sure that the project can be turned into a proprietary project at anytime.
The copyright holder can decide about the license. As long as only one entity holds the copyright, this entity is free to change the license. This even works if the project is licensed under a copyleft license like the GNU Public License (GPL). Such projects might look like “open-source”. Fine, the source is open at the moment. But it might not be open anymore tomorrow.
Interesting thanks! But is it possible to change the license of already published GPL or MIT code? Like, I get that if they make any additions to the code they can say that from now on it’s all rights reserved. But the versions that have already published under GPL or MIT cannot be unpublished, can they?
Some projects let individual contributors retain the copyright on their contributions. When a project is run like this, for better or worse (usually for better) it becomes impossible to re-license it, as it is usually impossible to track down every single contributor and get them to agree to new terms. This is the condition of the Linux Kernel.
Some projects demand that copyright is assigned to the organization up front, so the organization has the ability to re-license or dual-license the code down the road. This might also be done so the organization has standing to sue people who infringe the copyright. Notably, this is a requirement of the GNU project. This has resulted poorly for the end-users of some projects/organizations in the past though (MySQL for instance, which now belongs to Oracle).
