I am wondering why some TV shows will have the length of their series finale episode extended. For example, a sitcom's series finale can be extended from 30 minutes to 1 hour, and a drama's series finale can be extended from one hour to two hours.

The series finales of M*A*S*H (a 30-minute comedy series) and Lost (a one hour drama) have both lasted for two and 1/2 hours.

One notable show that didn't have an extended series finale is Everybody Loves Raymond; ELR's series finale was a regular-length episode (30 minutes).