Gotta remember the history of 990.....
In 1959 when it was created the engineering showed that Providence had no really viable AM frequencies available and FM was a weak, struggling infant. 990 showed up as workable for a Providence COL in either of two ways: A rooftop 250-Watt daytimer if a rooftop could be found downtown. There was some small possibility of it being fulltime but, at 250-Watts, why bother when the coverage area would be essentially vacant at night. The other was the monster 6-tower array in the boondocks, dumping the signal into the ocean. It could have achieved pretty much the same coverage with 25-kW or 50-kW (The FCC was only licensing values like 250, 500, 1kW, 5kW, 10kW, 25kW and 50kW at that time so 20-kW might have worked but was not a recognized power level). The decision to go with the full 50-kW was based purely on marketing hype..."Rhode Island's First and Only 50-killowatt Radio Voice...hence "W L (roman numeral 50) K (kilo) W (Watts). Advertisers, especially agencies, were impressed by power and hadn't figured out what "directional" meant in terms of coverage. More, everybody else in the market was trageting the lower teens so there was appeal in reaching a 25+ audience that actually had some money to spend. It worked. For a time. Operating costs were so high that it was tough to make any money and then along came FM and more sophisticated time buyers. Beyond that, it's all just a downhill slide.
What I find interesting is that nobody has ever bought 990/Providence to put it out of its' misery and make it possible to power-up some other station; perhaps Groton's 980.