Just as real estate has its "location, location, location" rule, radio has a "signal, signal, signal" dictate.
If much of a market can't hear you, you can't compete. In such cases, if you do end up doing something good, someone with either a bigger signal jumping your format or an FM taking it on.
A "reality check" is not the same as only looking at statistics. The reality is that there are an average of less than two AMs in each of the top 100 markets that covers at least 80% of the population day and night. Some markets have a couple more, some have none. And that means that most Top 100 markets are overloaded with stations that can't compete.
The further reality check is that, irrespective of programming, AM does not sound as good as FM or even as good as a 128 kbs stream or mp3. Who the heck is going to listen to AM if there are an almost infinite number of options that sound better and are more widely receivable?
As those who grew up on AM age out of the salable demos and as noise levels increase further, AM will be even less attractive.
Add in the fact that ALL radio has a lower revenue pool and more stations and there is a reason why nobody is putting much in the way of resources behind any but the best AM signals.
In Spanish, we have a saying, "A monkey dressed in silk is still a monkey".