Well, I am tired of listening to Salt Lake City, Denver, Dallas, Chicago and Minneapolis at night while not much from Iowa AM stations. Maybe all ISU sports should move to FM like 104.9.No, it's not stupid.
Here’s good explanation from the FCC as to why AM radio stations reduces their power at night. A thing I learned in college while I was studying broadcasting is that the further down you are on the AM dial, the further your signal can go. KWMT because of their location on the dial, has the single largest daytime coverage area of any radio station in the state. That would also explain why reception of Chicago radio station is the norm in Iowa from about Des Moines east.
Why AM Radio Stations Must Reduce Power, Change Operations, or Cease Broadcasting at Night | FCC.gov
KXNO operates at 5,000 watts, but operates on a directional night-time attenna, here's KXNO's coverage map: KXNO-AM Radio Station Information
Actually, there are 2 50,000 watt "clear channel" AM stations in Iowa and even then, they shift their nighttime signal around to not interfere with other 50,000 watt clear channel stations that operate on or near their frequency. An example of this is Omaha's KFAB at 1110 on the dial, they are a 50,000 watt signal that shifts their signal to the west so as to not to interferre with KMOX out of St. Louis and another 50,000 watt clear channel signal in Charlotte, NC that operates at 1110 on the dial.