Linux came around at the right time when the Internet was going public and regular people had access to hardware that could run a decent UNIX. People latched onto it because it was free and an interesting project. The free BSDs were just late enough to the party that they missed out on the momentum.
All the proprietary UNIX vendors (other than SCO) relied on expensive proprietary hardware sales. Intel ate their lunch while they were too busy stabbing each other in the back to notice. Linux killed SCO because SCO was, quite frankly, overpriced crap.
None of this had anything to do with the license, other that the fact you could use it for free. It was all about hardware availability, the rise of the Internet, the wave of new IT people who had experienced Linux at home, and the fact that Linux on Intel was good enough to replace those pricy proprietary machines.
Now, you wanna talk Apple, there's where your code "theft" kicks in. But that's a whole different thing.