I think it is up to the game developers to make this choice and balance out if it's worth it or not.
I guess that is right, the developers should make a decision whether they want to invest in creating modding tools for their projects and keep it organized, therefore, it is up to developers in each case. By the way, even with GNU license, I believe it is fair to e-mail the original developer and establish basic agreement over any actions to be taken on own behalf upon their work. Communication, in general, is recommendable.