The reason is in part down to cost saving.
Build the car with all options and activate what the customers asks for.
If the customer wants it later, they can test it and then buy it if they want it. By the same token, a lease company will take the car at least specification and if the customer wants to add something, it is at their expense. They can then turn it off later when returning it to lease.
Also, next owner may not want heated everything, but may want Android Auto and ACC (auto cruise control) as they do lots of travelling, turn the option on instead of looking for this one specific car.
Replacement parts, 1x control unit instead of 4x different ones. The list is endless.
We were told about this a while ago at my dealership. Some of the newest 2022-built cars have this already. Sales Manager X6 has the buttons for ACC but not activated. He drives round town for tots if 8 miles per day, does not need it, but next owner can have it so makes the car more saleable.