Most of that was a leftover from the original days where Powel Crosley built WLW. Radio, AM/MW in particular was a national product with national advertisers. WLW was called the 'Nation Station' because it could be heard in major population areas and well into Europe. A lot has changed since then.
That's a bit of an exaggeration because even when it was 500 kw it only covered well parts of Ohio, Indiana and Kentucky. At night, it did well for about 800 to 100 miles in all directions, but that operations was relatively short-lived and ended by the FCC.
What made those distant stations successful was in a big part due to the national nature of network radio in the 30's and into the 40's. Many smaller towns did not have a station, and many more had just one.... often a Class IV.
If you were in Traverse City or Petoskey, MI, in the 30's you had to listen for Detroit or Chicago stations to hear the network shows.
There were no "Top 40" or fully music formatted stations then. People had great big console radios in the living room, and even the dials of some were marked with the "big" stations on their dials. In that era, ads in
Broadcasting Magazine showed night coverage and response maps because that listenership was salable to clients in that era; if that show on WSM got one letter from Oregon, for sure that was part of the claims made in their ads.
Agency clients would buy Red or Blue or CBS, but not so much local stations. Fewer stations and big coverage mattered.
There were even more local stations like KMA in Shenandoah or KNX in Yankton that reached farmers in huge, often multi-state areas during the day and then entertained their families at night with network shows. But as the nation... and the dial... filled up after WW II and the influence of the Musicians' Union declined, radio "went local" and music formats emerged, focusing on local retail accounts and not national network ones.