And not by raising price*

You already have all the customers you're going to get

If you can't raise prices, you can't optimize profits!?! Hospitals, "have all the customers" they're going to get, but prices go up (faster than inflation) every year anyway. Note that insurance companies are often regulated on their cost percentages, but if their payouts keep going up... they're profits can too! Ultimately, that may even lower their number of customers to only those who are most profitable. Win-Win!

I think it's kind of funny that some people think that "deregulated" markets are somehow magically efficient or competitive. Collusion and monopoly are inherently higher profit margin businesses and so incentivized by unregulated markets. Monopolies can be supply, transport, territorial, or temporal, but all optimize ROI.

Note that regulatory capture is yet another method of stifling competition and creating monopoly pricing power.