Have you ever listened to a child tell a rambling incoherent story, where they leap from wild idea to wild idea? Where there is no concern about plot holes or believability, nonsensical plot points are made up on the spot and then immediately forgotten, and asking "why?" is pointless? That's what the script of this movie is like.
Monsters fight as advertised, so that's something to enjoy. But the plot is so bad that it makes you feel dumber just for watching it (and not in a good escapist way) and the whole thing a disappointment.