[Big Business]

Its all a matter of money and training. Chuck Liddell would be stupid to go to boxing because he would be taking a pay cut and hurt his MMA status. The're have been a few that have tried it with mixed results.

Jens Pulver who was a former UFC Lightweight Champion did fairly well, but did not make any money and went back to MMA. Now,some MMA fighters will have boxing fights on small shows to help their standup and it does not count against their record.

Plus, I think boxing is rigged half the time for the big fights.