Firstly, the biggest payola scandal is definitely associated with the late 1950s rather than the 1960s or 1970s; DJs like Alan Freed and the television personality Dick Clark, amongst others, were investigated by a congressional committee in 1959, which resulted in Freed being fired from the station, and other DJs getting in hot water (e.g., the Detroit DJ here). It has been argued that the payola scandal was motivated by the general 'moral panic' around rock'n'roll; respectable adults did not really believe that teenagers would actually genuinely like to listen to this loud, primitive, rambunctious music, and they suspected that it was being fed to kids because of nefarious types giving and taking bribes. I mean, would anyone ever have really wanted to listen to Chuck Berry's 'Maybellene' if Alan Freed wasn't given a songwriting credit (thus encouraging Freed to play the song incessantly on his very influential show)?*

In truth, in some form or another, payola - at the level of music industry people attempting to influence influential people into giving some songs more prominence than others - has always been a part of the American music industry. Including the parts that seemed more respectable to the congressmen of 1959. The 'song plugger' was a job in the days when the music industry made (more of) its money through sales of sheet music rather than records; song pluggers would attempt to place new songs with popular musical acts. Going forward in time, beyond the 20-year rule of this subreddit, there were also payola scandals in the 2000s. The conventional wisdom in the music industry these days is that promoting a new song in the music industry - getting it on the right radio playlists, getting it to have the proper prominence on streaming services - is an expensive endeavour indeed. We're talking seven figure sums. What that money is spent on, exactly, is all a bit mysterious, but you are, I am sure, capable of basic mathematical calculations.

The problem for the music industry is that, on the whole, people don't like new music...it just doesn't (yet) have that familiar ring. Even if it's great music. Famously, a record industry executive told a New Yorker writer a decade ago that (now that SoundScan and the like have equipment allowing them to know exactly when people change the channel, without needing them to write everything down) on average pop music listeners give a new song about seven seconds before changing the channel. While perhaps listeners to current pop music in the 2010s are obviously not the same as listeners to current pop music in the 1960s, radio programmers (or disc jockeys, back in the day, who actually physically jockeyed with vinyl discs while talking on air and used to have much more control over playlists than they did after the 1970s or so) have long been reticient to add new music to their playlists. They often need to be convinced to play it in the first place (unless it was the new single by, say, the Beatles, and so their audiences are probably going to like it judging by how much they liked the last 10 Beatles singles, etc).

So, the art of the song plugger (going back to the days when they had to convince a bandleader rather than a DJ) was to convince the right person that the new song had legs. That it was just the right thing for the playlist/setlist. If money greased palms, well, that showed that the record company or the publishing company were committed to the song (and how often would you, the DJ, really want to play a new song that the record company was a bit meh about? If they didn't think it was good enough to spend money greasing your palms, why would you?)

When it comes to massive fraud or targeted manipulation of the airplay charts - the airplay charts was always full of targeted manipulation. As far as the DJs were concerned, however, the music still had to sink or swim with the listeners. DJs were/are, after all, largely employed by the radio station in order to convince listeners that they should sit through the advertisements without changing the channel because the next song will be what they want to hear. If that's a song that they're only playing because of payola, there's only so much of a chance they can give it with no audience response before the DJ starts to worry that listeners are switching channels when it comes on. And if the audience just simply doesn't respond to the song, well, the record company guy will be back next week with another song from a different part of the record company, but with pretty much the same palm greasing.

So, broadly speaking, most of the time, a song (especially by a new artist) getting onto the airplay charts in the first place is probably often targeted manipulation in the payola sense. While the 1950s payola scandal showed a bunch of manipulation that was exceptionally blatant, there are less blatant and less obvious forms that still occur when payola might get record companies and DJs in political hot water. Payola directly leading to song staying on the airplay charts for any length of time, probably, is much rarer - that starts to get very expensive, especially if the song isn't selling records as a result.

When it comes down to it, American pop music is intrinsically the product of American capitalism. The record company wants to sell records, and airplay is a way to do it. The radio station wants to sell advertisements, and airplay of songs given to them by the record company is a way to sell advertisements by convincing advertisers that the right demographic will hear the advertisements because the music makes them want to stay tuned into the station. Major label record companies would have plenty of new singles each week. If one song tanks despite the payola, eh, there's another single to try next week. And as far as the DJs and record companies are concerned, encouraging the DJ to play the song using whatever means necessary is just part of that capitalist process.

*NB. Rolling Stone in 2004 voted Maybellene the 18th greatest song of all time.