It is open source. You are free to fork it if you don't like the terms for contributing to that repo so long as your fork remains open source, just as Apple did with KHTML, Google did with Webkit, and Electron and Brave did with Blink. If Warp were open source to begin with, people would have been free to rip out the things they didn't like in it and build upon the things they liked, benefiting the project that was forked to begin with because they can do that as well.