[Corvina]

Lol, what?
The bashing of other artists and idols in here is really bad.
Nobody of you can possibly know why somebody is popular or why somebody listens to an artist. I don't like idols much, I mostly don't even know their individual names, but they do have some great songs here and there with great production value.
You can also say the same vice versa - people just listening to other artists, cause they love the artist, not the music.
It is all about taste.
The most popular female idol group right now is Nogizaka46 actually, especially popular with the female youth, and they do touch some deeper themes with their lyrics.
You can find the results of regular surveys what's popular with the youth on Baidu e.g.

I agree with you guys that trends are cyclic and it's going to change again on a broader scale in some time, but just because you don't like what's popular right now doesn't mean it's bad.
And Kenshi Yonezu is absolutely huge right now over there, everything he touches turns into gold.
( I do think personally he's boring as well, just like Aimyon, but it's simply not my taste, just like Ed Sheeran and Billie Eilish here in the West - which are imo very similar artists. I'd agree that cultural "regression", for the lack of a better word, is actually visible worldwide, not only in Japan).