Trivia: All the original main cast members were in this movie except Susan Olsen ("Cindy"). Jennifer Runyon took her place. Two possible reasons that Susan/Cindy didn't participate: filming conflicted with her honeymoon to Jamaica and she was offered less money than the other cast members.
Suggested correction: According to all sources, it was just the first answer (the honeymoon reason). No confirmation anywhere about being paid less.
You should do some actual research before correcting people so you know what you're talking about. Olsen herself said in a 1993 interview about why she wasn't in the movie. "It came down to money and bad politics. I was asking for way less than the two other girls wanted, but they still wouldn't give it to me." Plumb and McCormick even tried to get Olsen paid a fair amount, but the show's creators wouldn't budge and started a look for a look-alike.
Yeah, right... it is never about the money.