This is a comedy
I think most people missed it, because the jokes are really subtle and none of the characters are funny or joking. The whole ridiculousness of everything in the movie is what is meant to be funny.
*Spoiler Alert*
Sharks climb ropes. The girl picks a hedge trimmer as a weapon. They smell gas after a shark bites through the roof of the car and the car blows up moments later. They stop tornadoes with bombs......I mean, come on, folks, it's absolutely silly. It's making fun of Jaws, Twister, and just about every disaster/animal swarm film in existence.
OMG....Fin jumps into the mouth of the shark and carves his way out. And it happens to be the one that swallowed the girl.
I'm pretty sure it was purposely made to be really cheesy just to mess with people. It's genius.