I'm sure that if Linux wasn't GPL, you'd have 'vendors' selling 'HP Linux' and 'Corp Linux' to their locked in customers in no time at all. The only reason Linux grew up to this point is that the vendors are forced to contribute back and cooperate (up to a point). Mind you it might also be the reason Linux is so bloated these days, but at least there is no vendor lock in...
As a small example, someone decided a few years back to release a "Arduino UI" over my own simavr[0] as an indigogo project. ie trying to be paid to package a demo I made (for free): he had screenshots, a few promises and no source code. I managed to email the guy telling him I wanted to see the source code of the whole lot and somehow, the project fizzed out.
If my project had been BSD, I might have seen someone making money from my project and associate my name with something that I had zero control on. When I give a project away, I want it to stay free for use, and I really hate to see 'packagers' who don't contribute anything at all move over and try to monetize it.
Same story as when I released freewares a few years back, I had a note saying it was NOT ok to package it on 'CDs' sold around.