If they don't care about reception quality then they don't need to factor anything in; the AM radio would be a trivial addition to the FM radios they already have. But they lobbyied against this because they do care, they'd rather have no AM radio than one that works poorly.
It's fuck-all hardware, FM and AM radios have been paired together since the 80s as an absolutely trivial expense; it probably costs them more to get FM hardware without the AM than to get both as a package. In fact their hardware is probably AM capable already, merely unexposed in the user interface. And buttons? Who is still making cars with real buttons for the radio?
I think the latter is significantly more likely.