What happened is that with the shutdowns, profits went from 2-3% to 20-30%. Some of that money was given back to consumers, but most went into an absolutely insane soft market where every carrier paid more than they ever had to acquire any driver they could.
This led to a lot of carriers having drivers on their books that they really didn't know how to price correctly. Everyone realized at roughly the same time that they had screwed up more than usual - and that was when drivers got back on the roads. Suddenly frequency and severity of accidents were up to historic levels because everyone forgot how to drive and is driving ANGRY.
So there's a double whammy, it's drivers they haven't insured before on the one hand and the drivers they do know how to price changing their behavior en-masse. So we've gone from once-in-a-lifetime industry profits to massive losses. For the first time, when the carriers tell the government the price is unsustainable they actually mean it. Hence the California shut downs - carriers are TRULY taking a loss on most policies they write and are trying to shut down new customer operations as much as legally possible. You'll notice a surprising lack of auto insurance ads on tv compared to 3-4 years ago.
Progressive's underwriters are so far ahead of everybody that they got a lot of their price changes submitted before everyone (the other carriers and the government) figured out what was going on. You can see that in many states where the prices are public, in an incomprehensible data format. So they have been one of the only carriers still getting new customers.
It's basically been a state-by-state showdown now between state insurance commissioners and carriers, and the commissioners are starting to give in. Premiums were up almost 20% last year nation-wide and it's only going up.