Any movie that has made money in the last 50 years.
Because they all do, and there is nothing short of Gaviscon or a sordid sex scandal that will stop the cycle. If you survey the number of James Bond film, the Rocky films, the Batman or other superhero films…you become quite despondent for the species. The fact that they succeeded the first time and have succeeded for so many times afterwards indicates the basic intelligence of the audience – the fact that the price has risen each time lets you know that P.T. Barnum was right.
I am personally stunned at the amount of money that changes hands in after-market spinoffs and merchandising for these things. I walk through stores dedicated to movie goods and look at price tags in amazement. The fact that there are actual stores full of the stuff is frightening. Of course the religious supply stores are also nerve-wracking, and sometimes for the same reasons.
For myself, I treasure entertainments that are self-contained. If they are not perfect, that is just the luck of the game. The fact that they play out in 60 to 90 minutes and need never be seen again is part of the appeal. I never seek a sequel or prequel. I am content now with Sleeping Beauty or The Sting just as it was.