They're under an affiliate rather than franchise model. I don't know enough about the differences to describe the differences other than to say that it seems to make Headquarters think they're unable to enforce standards once someone opens a gym.
I haven't done it myself, but to open an affiliate you need to:
(1) Write an essay.
(2) Pass their Level 1 certification class
(3) Have a website with a link to the Crossfit Journal
(4) Pay them $3000 (annually)