Rates go down when insurance companies can reduce risk.
Yes, cost savings in an oligopoly are always passed promptly along to the customers. That is a real thing that economic theory or practice says happens.
Some insurance companies may but there will always be at least one who will not. There will always be a customer base who prioritize privacy over rates and there will always be at least one company to serve that client base.
Insurance is an area where death spirals are common as the least risky leave the pool, driving up average risk. The issue is there is no way to distinguish "privacy guy" from "shitty driver guy". So all the people in that pool are given "shitty driver prices". But those shitty driver prices cover the average shitty driver. So, at timestep n+1, the least shitty drivers without the devices comply with monitoring to save money. At timestamp n+m, where m is likely to be a couple of years, the deathspiral is complete and there is no way to distinguish between privacy and people who intentionally crash into trees.
At that point, compliance, or opting out of the system, become mandatory.
But lest you still think that people prioritizing privacy are catered to in the market, I'd like to know what cell phone you use? what carrier? what ISP? (I invite the rest of Slashdot to ask more leading, and saddening, questions along these lines.)