Of course you can do business that way. If the heating costs $x, and half the customers pay for it but $5x is charged then that is a profit.
The alternative would be to make two sets of cars (with and without heating). Or four sets of cars if another similar optional feature is shipped like this. Or 8 permutations if there are three features etc
It can certainly be cheaper to install them by default even if not all customers pay to enable them. ie it is mathematically possible that their system is cheapest for both the manufacturer and the consumer. The alternative would be no different for us cold-bummed drivers but possibly more expensive for the toasted-tush drivers.