Nissan Leaf here. AM radio works fine.

Given that Tesla will add it for a fee(and older Teslas had it), I presume its removal is not technology-related.

That is not correct, you cannot add AM. The radio fee is for people who upgraded their computer hardware and want a new radio that is compatible with the new computer. The new radio does not have AM.

You miss the point: Tesla chose not to fit AM radios because it would have made suppressing the electrical interference so much harder. Hopefully this will change as the FCC starts looking closer at the E.M. interference from Teslas.

Apparently Ford is starting to remove them from their EVs due to struggles related to interference. I don't listen to AM that much in my EV (Mach E) but the few times I have tried it seemed to work acceptably.

it's gone from Volvo and I think some other cars as well (like BMW, Audi, etc)

One of our cars is a 2023 Audi e-tron and it has no AM radio.

My immediate question was, was it harder and more expensive to specify a radio module/part with FM, but not AM ?

It seems like a design flex and not an actual cost or UI affordance, etc.

It is annoying because sports broadcasts in the Bay Area are typically on AM.

The problem isn't in fitting an AM radio, but in suppressing the Electromagnetic interference from the Electric motors and circuity.

Hopefully the FCC will wake up and insist that they fix the interference, and not just hide it by not fitting an AM radio.