Leno refused to take part because the show will be rubbish.
Quote Leno:
"In my mind I can just see Jeremy lambasting Americans for what they did to his show. So I think: I've got to run away from this as quickly as I can."
"I like the show just the way it is. Jeremy and the guys are extremely talented, so maybe it would be an idea to do an American show similar to Top Gear but not with the same name, because I think it would be impossible to recreate or live up to the standards of the British show."
"I don't think you could be quite as freewheeling with your opinions as you can on the BBC, because sponsors pay for the programs. Sponsors would be unlikely to embrace any criticism,"
"Americans don't really see personalities like Jeremy on commercial television. They know that they have to be somewhat watered down. When Jeremy rips into some sponsor such as Ford or Chrysler, well, that's the last time they sponsor that show. Then what you have is 'the meeting' after the show, where they tell him to tone it down. That's just not what they do at Top Gear."