>The only thing that could be done with the hypothetically-still-bsd combined work that couldn't be done with the perfectly allowed GPL combined work is to add more restrictions, though, so I think my general point still stands.
That's true, but if I'm a person whose only goal in life is to maximize free software, I may still be rationally motivated to license my project BSD instead of GPL. A BSD-licensed project can sometimes attract more users. Of course, that is because some of them will use it in their own non-free projects; but in many cases, their project would have been non-free anyway, and they would have just used someone else's code instead of mine, or written their own. If they use my project, it makes my project's ecosystem stronger, which is good for free software.
One can certainly make that case, at which point it largely amounts to a factual question and I don't have the data to answer it.
"If they use my project, it makes my project's ecosystem stronger, which is good for free software."
Maybe. If they run with your code and build a proprietary fork with a few features on you, and users migrate over, your project's ecosystem may be weaker despite the code being used by more people, and it would be bad for free software. It's hard to say.
That's true, but if I'm a person whose only goal in life is to maximize free software, I may still be rationally motivated to license my project BSD instead of GPL. A BSD-licensed project can sometimes attract more users. Of course, that is because some of them will use it in their own non-free projects; but in many cases, their project would have been non-free anyway, and they would have just used someone else's code instead of mine, or written their own. If they use my project, it makes my project's ecosystem stronger, which is good for free software.