Audio problem: When Newton is telling Stacker what he saw when he drifted with a Kaiju brain, his lips don't match what he's saying in some shots.
Audio problem: When Dr. Newton and Hermann are with the baby Kaiju, Hermann says "Should be three," but his lips aren't moving at all.
Chosen answer: Because they are scouts for an invasion of Earth from another dimension. They are testing our response to their arrival and military capabilities and the best way to attract military attention is to attack population centers.
Grumpy Scot