Even if Johnson ran, he'd never win a Republican primary. He is too socially liberal for the evangelical/teabagging crowd.
Well 1st off it's New Mexico so the evangelical's are not as strong as elsewhere. Then there is the "too socially liberal" thing, the tea partiers main focus is on fiscal issues where he fits them perfectly. If not being a social conservative was as big a deal as your making it to be then Paul would have been taken out in a primary a long time ago given his districts location.