If they really wanted CC3 to succeed, they should have taken it in a completely different direction for the competition. Boxing is too time intensive and potentially dangerous to get anyone "big" to fight. No one with a lot of name recognition would be able to put in the time.
They'd need to do something like DDR or Just Dance, or some other party game. Set it up with the biggest names they can get. Don't make it an in person event, so the overhead on a venue is cut. Do an actual obvious percentage of PPV sales to charity (75% of the PPV cost goes to charity), and overhead is a lot lower when you don't have to spend money on real training, a big venue, parties, etc. You get something competitive, but "wholesome" in a way that boxing never could be, and it could be low key and low expense enough to win good will for actually being a charity focused event.
Of course, all that would imply they genuinely wanted to make money for charity, but it could have helped their reputations as well after CC2's failure.