Or is it? I think everyone enjoys the idea of long-awaited sequel, but it's rarely something that lives up to the hype. Any of the the recent trilogies which attempted a long-awaited fourth film have ended up falling flat. Granted, I think see Transformers IV is better than no Transformers at all, but it's clear the next, long-awaited chapter is rarely something that makes people happy. With the exception of Toy Story 3, Terminator 2, or Aliens, there's virtually no instance of a successful resurrection.
Why does it keep happening then? Is it money? Maybe....but there's something else. People want that nostalgia to live up to the expectations. Sadly, most things only exist in their time. While the Hero's Journey tells us that it's ultimately the same story told again and again, it's usually true that it must change quickly or be left for the nostalgia scrap heap.
(That being said, I hope Dumb and Dumber To is good. It might be funny.)