If any of the places that you frequent plays an adult contemporary radio station over the PA, you are still hearing that annoying Taylor Swift song "Shake It Off," currently #1 on the AC charts. Like an earlier AC #1, "Roar" by Katy Perry, it's basically an anthem for bratty Millennials who don't want to ever change themselves in the slightest to fit in better with their social environment -- to have to adapt.
Anyone who doesn't like you 100% the way you are, and tries to re-shape you so that your behavior will be more pleasing to others, is just a hater. Glib dismissal is the Millennials' ideal response to haters, so that they never take any criticism to heart, however small and however accurate. No adaptation, no growth. Perpetual toddlers.
Childish emoting can also be heard in the AC #1's "Roar," "Stay with Me," "Home," etc etc etc.
When did the adult charts become so kiddie?
Going back 10 years, most of the year saw two songs at #1. "Breakaway" by Kelly Clarkson and "Lonely No More" by Rob Thomas are nothing to write home about musically, although in tone they're merely adolescent or young-adult rather than twee or bratty.
Another 10 years back, and the songs are adult for the most part, again whether you dig the music or not (probably not). "Take a Bow" by Madonna assumes an audience familiar with the give-and-take in adult relationships, beyond bratty tantrums or adolescent infatuation. "Kiss from a Rose" by Seal is a little more adolescent, based on the theme of love as a drug. "I'll Be There for You" by the Rembrandts is more young-adult than fully mature. It assumes a social network, but the challenges that the speaker faces are just bad days, nothing really deep.
Then we arrive safely back in good ol' 1985, where none of adult contemporary #1's sound kiddie or even adolescent. "Careless Whisper," "Smooth Operator," "Everytime You Go Away," and "Saving All My Love for You" all come from a mature stage of social development, with all its trials and complications. Even the upbeat dance hits are made for grown-ups -- "Rhythm of the Night" and "Axel F". There's also the soft rock ballad "Inspiration" by Chicago, which however super-cheesey and grating it is, nevertheless is made by and for adults.
What does this change reveal about generational differences? The target audience for adult contemporary is 25 to 44 years old.
So it was the Boomers and late Silents who drove the success of truly adult hits on the chart back in the '80s. The late Boomers and early X-ers, as suggested by their AC tastes in '95, were mostly OK with growing up, though still preferring periodic indulgence in the adolescent or young-adult mindset. Early X-er preferences show up again in the 2005 hits, although the introduction of late X-ers into the target audience has made the hits more adolescent in focus. By 2015, bringing Millennials into the core audience has made them downright infantile.
The main factor here seems to be the level of cocooning or connection that the generations enjoyed while growing up. Social connection causes personal change, in a pro-social direction, i.e. growth or maturity. Folks who grew up entirely within the outgoing / rising-crime period of roughly 1960 to 1990 are the most comfortable with adult life. That would be the late Boomers and the earliest X-ers.
Once the cocooning climate began to set in circa 1990, growth after that point would not be as strong as if it had taken place during the '60s, '70s, or '80s. Someone born around 1970 would have the tail end of their formative years stunted by cocooning, but the end result was not too severe -- it was only the tail end of the developmental window, and the degree of cocooning wasn't so high at the very beginning of the shift.
The generation born around 1980 would be affected more during their young-adult years than adolescence. These people seem more inclined toward a teenage mindset. By the time you get to those born around 1990, they only grew up during the cocooning / helicopter parenting period, and have hardly matured at all, not even to the adolescent stage of wanting social connections, being willing to engage in the give-and-take, and honing their people-reading abilities. Again, you can hardly expect a different outcome from people who were socially deprived for their entire formative years.
You can go further back and see the cheesier, schmaltzier AC hits of the '60s, when they were catering to the Silent Gen, who like the Millennials grew up socially cut-off during the previous peak of "smothering mothers" and Dr. Spock-inspired shielding from threats to the ego. Competitiveness was at a minimum back then, though, so their kiddie sounding AC hits were not bratty, but twee and saccharine. Case in point: the mawkish "Can't Help Falling in Love with You" by Elvis way back in '62, which sounded much more emotionally adjusted and pulled-together when covered by UB40 in '93.