Almost all state governments made it so that you can't drive a car unless you have insurance.
The reason they did this is so that if you hit someone and cause physical injury to them or to their property, it's possible to pay them for the damage you did to them.
The government has decided that it is a good idea to make sure that people generally have a way of getting money from people that have caused accidents. We've also decided that it's in our collective best interest to allow people that don't have hundreds of thousands of dollars of cash on hand to be able to drive to the supermarket. However, because of these two conflicting goals, we need a third party that can pay in these cases.
Since it's a legal requirement to give money to a third-party when someone wants to drive, state governments have also determined that it's in our collective best interest to not allow for bad behavior by insurers in overcharging drivers for things not directly related to risk.
The reason for this is that making car insurance generally unaffordable to classes of people tends to exacerbate divisions in society, at least in the United States.
Further, members of minority communities do vote in elections, and will generally not support candidates whose position on insurance companies engaging in price gouging is "the free market will figure it out, sorry you can't afford insurance."
Finally, it cannot be taken for granted that companies always discriminate fairly when there are no laws to prevent them from not doing so. The example we see here is evidence of this. If Allstate is making pricing decisions not based on risk but based on willingness to shop, then that means that people are being unfairly overcharged; it just so happens that it's not as immediately offensive to our morals when it's "willingness to shop" vs. "being a member of a historically discriminated group of people".