Well, the SD card really helps to make updates easier and faster, but of course the car companies still want to make maximum money. Up until a couple years ago car navigation wasn't even on an SD card, it was just installed in a built-in non-removable storage unit. Updating it either required going to the dealer or buying a USB drive with the updated maps from the map maker.
At any rate, I mostly use Google Maps. It is far superior to any car navigation or portable navigation units. And it is free and you get much more frequent updates. I think Android Auto will put many of these map makers out of business in a few years.