Like the barebones Tesla 3 that existed on paper but was basically impossible to order. OE’s know most people will spring for that creature comforts.
The core idea is that if some amount of people want heated seats the most cost effective way to do that may be to add the seats to every car, then those who want it pay that cost. (So if 1/5 cars want the heated seats each car have effective cost of 5x the per car cost because for each person paying they also have to cover the cost to install the hardware into 4 cars that wont pay for it) However that cost is still likely much cheaper than setting up a completely new physical model (especially if you consider feature combinations). But if you enable this feature for everyone then no one is paying the "premium" price so the cost needs to be spread out across all sales.