Didn't they make a law that radios had to have AM and FM?

The only law of that sort I remember was the FCC requiring televisions to have
both VHF and UHF tuners, and they had to tune "with comparable ease". (In
other words, a UHF station had to be as easy or as hard to tune in as a VHF
station.)

I don't remember any requirement that tuners or radios had to receive both AM
and FM. The drift (ar, ar) over the years was towards FM, highly accelerated
by the introduction of stereo FM. If either band needed help, it was AM.