It's not just the Generational factor, there are objective quality reasons Top 40 Music today is inferior.
We have partly ourselves to blame. Remember all that music downloading going on in the late 90's era? Napster, Limewire? The Music Industry is also to blame, for being so incredibly late to the technological changes of the time.
But all that downloading was in fact theft, and it eviscerated the music industry. Objective proof: David Bowie had an album cancelled by his label in 2000 due to it being "too artistic". (and it was a kooky album even for him) Whether you like Bowie or not, this was a clear sign of how it was all headed downhill from there. Taking chances and being more creative was too risky even for big, established artists.
If an arty album was cancelled for David Bowie, imagine what it was like for unsigned bands. This led to the homogenization of music that we have today. This is also the reason concert prices skyrocketed - there wasn't any money in CD's anymore due to all the downloading theft.
And now today, it's swung so far in the other direction, you can't even post a clear Fair Use analysis video without a copyright strike. Yes, you can fight those strikes, but it's David vs. Goliath every time.
The other thing that has ruined music is Auto-tune on voices, and the "quantization" of rhythm and instrumental parts. You're rarely hearing human beings performing music, in today's music. There are notable exceptions, such as Adele who somewhat famously had a noticeably flat note in one of her 2021 hits. (I have no idea which song, sorry, I'm not personally interested in her music but commend her for actually singing, and she is a good singer)
But not only is most of today's music Auto-tuned and quantized, and I really hate to tell you this, but they're starting to do it retroactively to classic music as well! This has to stop!
On top of all that, current music as well as classics are being dynamically compressed so heavily that just listening to music with that treatment is scientifically known to cause ear fatigue, in the same way that TV (if anyone watches that garbage anymore) commercials are harsh and loud. Dynamics is one of the 5 Elements of music, so dynamic compression objectively attacks musicality.
As a Musician, vocalist, teacher, I'm beyond disgusted at the walking zombie that is music today. Country is no longer country, Rock is nowhere to be found, and the dominant form of Hip-Hop sounds like a Casio keyboard auto-rhythm, some jerkwad rapper, and the spliced chorus of an actual song if they want to make it into a "hit".
Fortunately, this has had no affect on actual, real Musicians, who still exist, play, and write new songs all the time. But Radio is beyond dead, and people rarely buy the CD's that were the lifeblood of the independent Musician 20 years ago.
The only Musicians "making it" today are young, beautiful women on Youtube that get millions of views playing their instrument. Some are quite good, but this is ultimately demoralizing to know it ain't their sound or creativity that is pulling in the ad revenue. I remember when overt Objectification of women was a bad thing, now it's considered "empowering".
sigh