Licenses that allow more collaboration end up winning, and permissive licenses allow more collaboration.

That said, the source-availability requirement of the GPL did help kickstart things.

In the 80s every unix vendor had their own closed source version of everything. The GPL - through the requirement of source availability - helped flip the industry over to collaborative building. It would’ve never gone that way if those working in the open did it under permissive licensing - that would have given closed-source vendors free labor and discouraged those working on free software.

Nowadays it’s about velocity. In domains where collaborative building is producing more better software faster, it’s more expensive to work behind closed doors than to take others’ work for free. So you may as well use the open thing. And then when you want to add features or fix bugs, it’s a hassle to maintain your own fork while integrating new work from upstream. So you may as well upstream your work too!