I recall being a fan of KFJZ back in the mid-70s. Very well programmed, good talent and a very ample commercial load.
I got my first fulltime on air job in 1978 on the border. By the time I returned to the metro in 1980, KFJZ was still top 40 but the talent sounded more small market and the commercial load barely half what it had been maybe 4 years prior when I was listening to the likes of Mark Stevens (later Stevens & Pruett of KLOL fame in Houston). The former dominant AMs fell and fell quickly to the FM dial. It likely didn't help that KFJZ FM, Z-97, had been top 40 for a few years, launching commercial free for, I think 3 months or so before airing commercials. The first letter to arrive when the first commercial aired with the time and business name won, I think, $10,000 (maybe $25,000...memory if fuzzy). Z-97 made such an impact their competitors even addressed it. I recall the evening jock on KLIF fielding a call from a listener who asked about it. The jock said 'they will have commercials soon enough'.
Radio in general is going the way many AM stations went once FM listening took over.
I'm lucky. The North Texas station I work is insanely popular given there are 50 signals you can get on your radio. We rely on local businesses and they feel they must include us as part of their marketing because the station has just over 1 in 4 in the county listening. I've worked stations where I had to explain the station I worked for when cold calling. I say who I work for or they see my shirt and there's instant respect. Here I walk in a business with my shirt with station logo and about 1/3rd of the time a customer of that business says hello and says they listen. Those shirts are a hell of a sales tool. I am not saying what we are doing here will change radio. The truth is, we are not a normal station. There are not a whole bunch of stations like us.