For what it's worth: I used to belong to SRS, (Songwriters
Resources and Services) out of Hollywood. They had guidelines to assist with the promotion and marketing for musicians wishing to sell their material to established recording artists. The list of the people involved was a virtual who's who, of very well known and respected, successful people in the recording industry, and they covered about every type of music being done.
They would send out monthly bulletins, of recording artists, who were in search of material, with descriptions of the material and who would be interested.....(Some of you may wish to check them out)...
One of the fliers, which was more like a little booklet, to help writers and composers with their submissions, and what they were looking for, (and what they WEREN'T looking for) and the types of music that the producers pick from. Now this info was based on that time.....90% of all music submitted was of a 'religious' or spiritual in nature....7% was labelled 'meaningful'...3% was 'commercial'.....it was from that 3% that the music submitted, that was drawn from!!!!
So, if the music you listened to seemed...umm...'immature', it is because that same 3% (commercial), had their target audience at 13 to 17 years of age!!! ....and most of that crap was done by groups that sang about having problems surviving puberty!! (....and a lot of the 'artists' seemed to have that same problem).
...and that is what 'Top 40' is all about....teeny-boppers spending lots of money on junk, that also takes them a LONG time to outgrow!!!
...but eventually, some do....
I also had a close friend, Giorgio Tozzi, with his wife Monty, were vocal coaches....their clients included, Neal Diamond, Robert Plant, Frank Sinatra, and Barbra Streisand, among others..(you can Google him to get his bio...he just recently died, in Arizona, but I knew him when we lived in Malibu, California).....He had a great line:.." The sixties was a time when mediocrity was chic".
.....and other than a few artists and groups, he was dead on the money!

GfS