Sure, copyrights are still in effect and can be sold to other parties. One reason holding copyright over open source code is important is license enforcement. The benefits of holding copyright over code is why the FSF wants copyrights assigned to them [1].

[1] https://www.gnu.org/licenses/why-assign.html

The code is there for everyone (who respects the license), but you also buy the brand, the name, the guys working on the project (aka talent acquisition)...