Is this related to the temperature in the car, by any chance? My seat heaters do not come on automatically when I turn on the heat remotely through my app, unless I had them on previously. With that being said, "extremely cold" here at night is 31 degrees, and my car lives in an insulated / drywalled garage, so it is usually no colder than 45 in there at night.
My understanding was that the seat heaters are much more efficient than running the actual heater, and help contribute to warmer ambient air inside the car (raising the temperature inside the car faster than not having them on), so if the goal was "most efficient use of the battery in warming the car" thats why they come on when its "cold".
Both of you live places where it actually gets cold, so I believe the seat heaters come on to warm up the car faster (so you can turn off the heat if you want) thereby decreasing total battery usage in heating the car overall.
Thats what I got from reading around here, anyway, and it would explain why my seat heaters dont come on automatically (because its never REALLY "cold" here as people with real weather would know it, even though we bundle up like we are in the arctic if its colder than about 50 degrees, and thats all people talk about at work if its that "cold"
).