Why this fight?
Because it will sell, and because there is no good reason NOT to do the fight.
Tito wants a last fight in the UFC, and he wants one that will sell. He’s a proven draw with a cut of the PPV, so fighting someone on FX or even Fox isn’t worth the check a 800k buyrate will give him. Forrest gives him a name opponent, no matter what- FG holds that “former champion” tag. Ortiz is a draw, Forrest is a draw, making money one more time.
Ortiz also wants to go out a winner, and Forrest is a winnable fight for him, I personally think he lost both fights, but a strong case can be made that he won both as well, and Forrest does give him a bonus- Tito is not going to be knocked out by Forrest, Tito can stand and bang all day with Forrest, and roll around on the ground if he wants to as well. Why take a chance with an opponent that can drop you (Rampage, Lyoto, Shogun) or submit you, when you get a guy who is more than willing to let you dictate the fight and follow your lead?
Forrest on the other hand, is in a no-win position. How many fights is he from a title shot? 2? Maybe even 3? His frame is too big for 185 as well. He is a proven draw, but his style really makes his matchmaking hard. Joe Silva can’t afford for him to get a long losing streak, nor just throw him against bottom feeders just to get a win, either. Tito is a good fight for him, as who in the 6-10 range would be a good fight? Even if Griffith wins, his best bet would be the winner of the Bader/Rampage fight, or a bout with Lil Nog. Lose and its Schaub or Mike Russow on FX.
The other bout I’m interested in, is Frank Mir vs CAIN. From Cains side, this ones easy- watch Carwin demolish him and repeat. This is a win over a legit top 7 HW and a rematch with JDS for Cain. For Mir, this fight is a no-win. If he stuns the world and wins, he STILL is looking for another win to get a title shot to me. He might get a shot with just a win, considering how thin the division is, but say Barnett wins over Cormeir, who gets the title shot? Mir or Barnett? Say Cormier beats Barnett and then Werdum. DC or MIR? If I was Frank, I’d rather take my chances with another huge banger like Bigfoot or Werdum then setup a Cain fight for a definative #1 spot, and hope Overeem is the champ.