-He hates it in hell
-Likes to fight people
-Goku agreed to revive him with the dragon balls if they win the tournament. If he's lying or not is yet to be seen
-The whole universe (That includes the otherworld and hell) will be erased if they don't win

What sell this is less of my brothers so-called, "redemption…"
…more of, let's watch the genocidal space emperor go shoe shopping in a button-up and khaki pants with his mortal enemy's wife.
Next we should have Cell teaching aerobics classes and have Broly be a transvestite…
OH WAIT A MINUTE…