I can’t speak for Zed’s specific case, but several years ago I was part of a project which used a permissive license. I wanted to make it even more permissive, by changing it to one of those essentially-public-domain licenses. The person with the ultimate decision power had no objections and was fine with it, but said we couldn’t do that because we never had Contributor License Agreements. So it cuts both ways.
You seem to be assuming that a more permissive license is good. I don't believe this is true. Linux kernel is a great example of a project where going more permissive would be a terrible idea.
Saying I believe one specific project—of which I was a major contributor and knew intimately—would benefit from a more permissive license in no way means I think every other project should do the same. Every case is different, and my projects have different licenses according to what makes sense. Please don’t extrapolate and assume someone’s general position from one example.
It's reasonable for a contributor to reject making their code available more permissively