FM was more popular for music since it is higher quality, while both work fine for voice, and AM licenses can often transmit further. So it made economic sense

FM was more popular for music since it is higher quality, while both work fine for voice, and AM licenses can often transmit further. So it made economic sense for talk radio stations to buy AM licenses instead of FM. That said with fewer people listening to music on the radio these days, it is becoming more common to find talk radio on FM.