Doesn't have to be free to get mindshare, though it helps.

Multics lost the mindshare battle when Berkeley started distributing BSD. They would have had to go open source / free way back then, in 1978 or so.

Mindshare, mindshare, mindshare. That's the key for this sort of thing.

Oracle, for example, locked in SQL mindshare long ago. I'm not sure that Larry Ellison understands this -- after all, he (well, Safra Katz) killed OpenSolaris when that was a vehicle for gaining mindshare. But then again, maybe it was too late for Solaris anyways.