Even Dr. Dre is disappointed in modern music.

this gets more into Art Crit theory, but its a matter of taste vs mechanics (mechanics being 'what is ____ trying to do')
when your inside content creation (whether making it or being active participant), there is a certain degree of what works/what doesn't work - what are you trying to express and how well is that landing??
when you're inside that, you are answering those questions both actively and passively
after you've been out of the game, you're not really asking/answering the question - you're an outsider
so the only real response should be of taste - 'i like it or I don't like it' - you're not evaluating the music bc it's not for you
...
or consider it this way
80s fashion - esp for women - had a fairly specific silhouette emphasizing shoulder and hips by cinching the waist
it was a look very much tailored to the male gaze (and a certain male gaze at that)
now imagine Janet Jackson telling Zendaya she doesn't know how to dress
Zendaya is not trying to model JJ's silhouette and she is emphasizing different things and the idea of a woman's body has changed significantly in the intervening decades

I'm not sure this answers my question unless your response is that you can't know what is or isn't good music and nobody else can either. Artistic nihilism to I thik coin a phrase.

And if that is your answer, I agree. Art, including music, is purely subjective in terms of what is "good" or "bad". There is no intrinsically good or bad art.

Some art or music is mechanically better than others. Some musicians have greater skill than others. Some painters have technically better skills than others. But whether it is good or bad is subjective.