Injuries and illnesses have and will continue to effect the UFC for the time being. I think 2010 will be much brighter than the latter half of 2009, and, as was said, UFC 107 should prove the value of a championship match. Having four out of five of your champions on the shelf is bound to hurt business. Then there's the host of other injured fighters, most of them big names or up and comers. If there's a slump, the aforementioned is your cause.
Ticket sales and increasingly high prices are also likely a contributing factor. These celebrities and fighters can likely afford to pay top dollar for a seat, but your average fan will likely shy away from the idea of spending 450 dollars for a so-so seat. The fact is, UFC can well afford to lower its prices, and until it does, you're likely to see a certain amount of tickets left unsold. Which begs the question... sell for less, or don't sell at all?