probably due to them saying "a true story" that people wanna go and see it. My sister saw it and found it completely rubbish. They filmed it like it was in the blair witch project (sort of amateur filming type thing), and the whole thing was pretty naff.
I wasnt going to see it anyway. I didnt think the trailer was too good, because it seemed to me as if they showed all the good bits in the trailer and then if you watched the film there would just be padding of water and shark fins around the good bits.