It is doubtful that disabling FM would benefit their bottom line. A person is either going to stream, or not stream, based mostly upon their preference for content. Given that mobile data is very pricey, I very much doubt that many people are going to change from FM radio to streaming just because the FM receiver is disabled. (At least outside of places where they have access to WiFi.)

As for AM requiring longer antennas, that's true. However, people are plugging in headphones as antenna's anyhow. Seeming as AM antennas are about half the size of a pencil, and dirt cheap to make, I could imagine using such an antenna while at home or in the office.