Movie sequels

There are other movies where the original is mediocre at best, yet the keep making sequels. Each sequel loses a few of the original actors.
Ever see Tremors with Kevin Bacon? How about Tremors 4? How about From Dusk til dawn 4. Theres all the I know what you did last Summer movies that went on like the Scream sequels.....
Final Destination
American Pie
Then there are the movies that actually ADD characters...
Lethal Weapon
Fast and Furious