The Linux kernel adopted Bitkeeper before git and it never spread out from there. It's not that many people working on the kernel.
git growth was very symbiotic with GitHub growth. I don't remember why GitHub became popular in the first place. I think it was the Ruby community? GitHub was one of their own during an explosion of Ruby on Rails and successful startups using it.
Maybe? But this is an argument you can make about most technology adoption (silly recent example: USB-C adoption obviously buffetted by Apple showing up and saying "it's all this now" and having a bunch of people willing to swap everything out for it)
git growth was very symbiotic with GitHub growth. I don't remember why GitHub became popular in the first place. I think it was the Ruby community? GitHub was one of their own during an explosion of Ruby on Rails and successful startups using it.