Also, probably a first-mover advantage, early on. Linux, the GNU toolkit, etc. come on to the scene and are based on GPL, so a lot of developers's first experi

Also, probably a first-mover advantage, early on. Linux, the GNU toolkit, etc. come on to the scene and are based on GPL, so a lot of developers's first experience with open/permissive/whatever software licensing was GPL. Over time, though, developers become aware of alternatives, and for various reasons, many use them.