Because they can. They don't even have to justify it. My car insurance goes up every year despite no accidents on my record. I look at competitors rates and they are even more expensive. Across the board they are just raising rates.

And we as consumers have no recourse, because we are required to have car insurance to drive, so it's not like we can just boycott them. Would not be surprised to learn that there is collusion going on between all the auto insurance companies to keep their rates roughly similar and raise them all at once.