I actually like (good) movies that go beyond 2 hours; however, as far as the “why” of sequels, it is quite simply.  Doing a sequel has less financial risks than doing a new movie altogether.  In a new movie, you are still unsure how many people will show up, while in a sequel that generated good revenue, you can be assured that the next one will have something similar (since those that didn’t like the first won’t go see the second, but those that liked it will have told their friends.)

I don’t like long movies, 2 hours is my time limit.  I can’t sit still much after that.