I feel like price discrimination is more of a factor here. To maximize revenue you want to charge an individual the maximum amount that particular individual is willing to pay. Which is going to be a different price for different people. You still make profit from everyone but make more some from than you do others. But how can you charge some people more and some people less for the same product? Well you have to come up with some arbitrary reason that seems fair. Well you're paying more because you get heated seats, that's fair right?

But when it's cost effective install heated seats in every vehicle, how can they use this as a way to achieve price discrimination? "Hey you got some money and can afford it pay this subscription fee to enable the heated seats!"

Sure fixed costs are a factor, but distributing that cost equally over all vehicles sold is simpler and makes more sense. I mean in the end we are talking about different methods for a company to recover the costs of doing the R&D and product development, integration with an an assembly line, etc. after all. The cost is obviously paid upfront, the per unit costs isn't a factor since it's being put into every vehicle. So if unit costs are factored out this is entirely about implementing price discrimination when recovering fixed costs.

And price discrimination is always just shenanigans that only work when a company gets away with it. In this case they didn't.