The legal--or even common--definition of "fault" isn't at stake here. The fact of the matter is that they've got mountains of data that say that if some "random crazy fluke thing" happened to you, then you're more likely to have it happen again. Because that's what the data tells them. Heck, it could be that you just live in an area where people drive like crap.

Look at it this way: let's pretend an accident (regardless of fault) actually lowered the chances of a subsequent accident (maybe you're scared into good driving), and the longer you drove without an accident, the more likely you are to have one (maybe you become complacent or something). In this situation, your rates would go down when you got in an accident. Because it's not that they're trying to punish you, but rather they're trying to just charge based on the X% chance you're going to be in an accident, plus Y% overhead/profit.