Why do they continue to make prequels?

I hate prequels. Its like the producers and directors forgot to make THAT one FIRST, instead of making a movie and however many sequels, then going all the way back and going before the first movie. People want to see what happens next, not what happened already or how things came about. Thats what the first movie is for. Examples would be....Wolverine X-Men Origins (Why didn they just continue the story line, the xmen universe has so many sagas and storylines they could have branched off into...Apacolypse, Shiar, New Mutants, etc). Underworld Rise of the Lycans (why didnt they just make Underworld 3). Hannibal Rising (That was just some BS. Why did they just make Hannibal 3, they had the perfect ending in Hannibal, he was going to Asia, so they could have had a story with him in Asia). Those are just a few (exorcist is also in there). So whats your opinion?