If I recall correctly 1960 era FCC rules for the major broadcast ownership groups allowed for no more than seven AM/FM radio pairs per city, seven TV stations total for the entire country. If you owned a major news paper that was also considered for what your total ownership per market could be as well.
And if you wanted to reach lots of people, you had to have a paper or a radio or a TV station. Papers were limited by the cost of operation vs. available revenue. Radio and TV by both economics and the number of possible spectrum allocations.
Today, audio and video streams as well as podcasts and news/opinion websites have no limit. So if I want to start a "radio station" online dedicated to one city, I can do it by tomorrow. Maybe I want 10 "radio stations" with different formats, all targeting that city. And 10 more targeting another city and ten more...
I can do that, with a relatively small investment, instantly.
AM and FM radio are not a silo that is isolated from everything else. They are the weaker element in audio sources, in fact, as they need lots of ads to sustain themselves. A stream with a subscription fee can do that with no ads and a wide variety of formats. Look at Sirius/XM!
With the above mentioned ownership caps, local radio ownership was allowed to thrive. Most of the local ownership was on the FM side of things as AM radio was king during that time period and the larger ownership groups were still trying to figure out how to monetize the FM frequencies across the country as most were either classical or easy listening elevator music formats.
Most of the early FMs were owned by AM stations. FM operators tried lots of formats between 1940 and the late 1960's. It was not until FM radios could be made without paying the Armstrong patents, until FM stereo was authorized, until the FCC required the ending of most AM-FM simulcasts that FM "took off".
And that "easy listening elevator music format" was renamed "Beautiful Music" in the very late 60's and stations with that format were often #1 or near that position in the ratings.
The ownership rules were basically done away with mid 90s. Ownership groups were allowed to buy up properties and consolidate into larger conglomerates. Syndication became the norm throughout the 80s and the 90s.
"Syndicated" programming was called "Blue" and "Red" and "CBS" from the late 30's onwards. It's nothing new for stations to get programming from outside the market.
Technology in the late 60's and 70's allowed stations to get formats... whether Bonneville or SRP or Drake-Chenault and over a dozen others... and play them off tapes locally. Satellite distribution brought more options starting in the following decade.
The conglomerates also owned the syndication structure as well dictating what programs were to be fed the local stations in the chain.
SRP (Shulke) was privately owned, as were nearly all of the syndicated format creators. The only significant one that was tied to a broadcast group was Bonneville, which only owned a small group of stations.
This paved the way to the larger conglomerates we have today of Audacy, iHeart and Cumulus all of which have filed for at least one or two bankruptcies in recent years, cutting cost, laying off talent, gutting live a local programing in favor of voice tracking.
That has nothing to do with the origination of programming. The financial issue has to do with changes in listener preferences. In 2020 the average Persons Using Radio was around 20. Today, Persons Using Mass Media (radio and its streams) is around 5. That means that listening is off by 75%. And revenue is off proportionally if you adjust for inflation.
This is the broadcast industries definition of progress.
There is no progress when more and more people want to listen on demand or to a variety of streamed sources.
Reminder: when consolidation happened in 1995 half of all stations were not profitable. The industry needed a solution. And consolidation worked for about a decade and a half until we had the combination of the introduction of the PPM (it showed about a third lower listening levels), the Great Recession and the introduction of the Smart Phone (giving access to thousands of "radio stations").
Radio was the "victim" of this, and you are blaming the victim rather than the causes.