It's because it's "utility function" prioritized maximizing "points" first and foremost and points are awarded only or at least primarily by hitting its targets. So, according to it's core programming, it's primary objective is to maximize points.
It feels like whoever did this knew this would be the result and wanted to make a point. At least they definitely should have known after the first incident, but instead they just told it, it would lose points if it killed the human operator, so it got more creative by destroying the infrastructure around the human... a better way would have been to change the order of its priorities, or change it so that it gets points by receiving instructions by the human every x minutes and losing points if it does not - and have those points be worth more than the secondary objective of destroying targets.