Their rationale is that the show's quality won't go downhill. It leaves people wanting more of the same.

Especially on Disney where the kids grow up. A 16 year old Raven or Lizzie living at home it cuter than a 23 year old Raven or Lizzie living at home.

Also as the audience for the show matures they lose interest. well this applies to Disney moreso. Characters should evolve and change just like kids do in real life.

With UPN I think that they just don't wanna pay actors big money. So you lock em in for Five years contigent upon ratings and what could a person do? Can't wrangle and hold out for a million per episode like they did on Friends.