That only applies to people who don’t own the copyright. If you wrote the original code base, you can license it GPL, but continue to sell it under closed sourc

That only applies to people who don’t own the copyright. If you wrote the original code base, you can license it GPL, but continue to sell it under closed source license as well. On the other hand, if someone forms it under the GPL, and adds some additional features, the original code base cannot pull those features back in the original closed source project, without ceasing to distribute the whole thing as closed source. Choosing GPL effectively forms your code, and further code added by others can no longer be added to the “proprietary” branch. But you can continue adding code yourself in parallel in both branches.