It was interesting that Ford could add it back in with just a software update. That tells me that the RF hardware around 1 MHz was never removed and it is just a matter of adding a very simple piece of demodulation software and a couple of menus to the radio. I bet that they don't even have to do that on current models but just have to flip one configuration bit in their radio setup.
Comparing what it takes to demodulate AM versus Bluetooth, WiFi, FM or even the keyfob security radio shows that the software for AM is trivial.
You sum up my thoughts on the matter. So much of what happens in a modern car needs filtering from the noise of the drivetrain, that AM needs it too seems like just an excuse. Some something else is the real reason behind removing it.