They can restore the AM radio band with a software update. Maybe it doesn’t work as well if they didn’t put enough shielding or filtering in but activating it in software tells us that there is something other than cost driving the decision to remove it.
As far as the cost of noise filtering, I would think all computer and communication systems in the vehicle would benefit from have good power filtration to protect from the electric motors’ noise. Given the average cost of a new vehicle is north of $40k, $100 for noise filtration seems trivial.
You would be surprised at how cost conscious the automotive suppliers can be. I did some work for Ford around 2001. The engineers went through board schematics with a fine tooth comb and removed anything that wasn't absolutely necessary. A single resistor times 250,000 vehicles is significant money. The kind of resources necessary to mitigate RFI problems is often orders of magnitude more than a few resistors. Taking the AM radio off the table to dodge the mitigation costs is certainly an economic consideration.