If you look at the ratings for major markets, you'll find at least one AM station in the top five in almost every market, often the marlet's heritage news/talk station at #1.....some markets like San Francisco usually have 3-4 AM stations in the top 5 (partially due to the topography of the area).
Of course, if you're a media buyer and looking for listeners in the 18-34 demographic, AM "doesn't exist" lol.
(Can you tell what industry I spent most of my life in?
)