Money determines sequels.
I was talking to Tom Hanks last night*, and he was explaining (in the same way that Matt Damon has previously) that VCRs created the gravy train - he said that Bob Zemeckis said to him, "Domestic pays for the film, international takes care of the other costs" and that then home video is where you cleared up. Then, you did a straight-to-video sequel because you already had an audience (The original plan for Toy Story 2).
* In the sense he was talking and I was in the same large room listening.