Because ticket prices determine how much money the studio gets. Distribution deals with theaters usually (and especially for really big budget films) have the distributor (in this case Warner Bros.) getting a percentage of the ticket price (usually around 90% for opening weekend and declining each week the movie runs). The more money the studio makes, the more chance that there's gonna be a sequel.

whomod said: I generally don't like it when people decide to play by the rules against people who don't play by the rules.
It tends to put you immediately at a disadvantage and IMO is a sign of true weakness.
This is true both in politics and on the internet."

Our Friendly Neighborhood Ray-man said: "no, the doctor's right. besides, he has seniority."