This seems a bit of a chicken and egg problem... why would the early adopters have chosen Linux, before others had been forced to contribute back their changes? The first company to adopt it wouldn't have received any benefits, only an obligation. Why pick it over BSD?
I think there were likely other factors that made it win out.
They would also get the "promise" that the system they were betting on would also get contributions from other companies, making a safer long term bet.
I think there were likely other factors that made it win out.