The incentive is NOT to make the most money. It is to charge just enough that there is very little room for a competitor to slip in a lower premium for the same protections. Thus, if you are deemed to be an expected cost is $1K/year driver then your premium should be about $1.1K a year to leave them some protection against the high-side risks (protection they usually get through re-insurance, but that's another concept and we don't want to overload the wet-ware circuits). Conversely, if you are deemed to be an expected cost is $10K/year driver then your premium should be $11K a year and I bet they just hope someone else comes along and offers you a better deal.
But "increasing the total sum they get from premiums" is not even a first order approximation of the TWTWW (the way the world works).