If I recall, the zeitgeist then was that bitkeeper was a necessary evil. My guess is that git would have come into being eventually in any circumstances short of bitkeeper becoming free software, and maybe even then. Distributed change management is such a critical component of the kernel development process (especially for Linus and the other maintainers) that relying on someone else's software seems suboptimal.
The reason Bitkeeper dropped the kernel was that certain kernel devs had started writing free software to interact with the kernel repository (they wanted to be able to perform certain tasks that bitkeeper couldn't). Had this continued, we would probably have ended up seeing a free version of Bitkeeper.