If new users are not taught by existing users what the existing users like and think should be upvoted, then what is upvoted will naturally shift over time.
Long-time members may consider that a deterioration in "quality". Quality is of course subjective, but I suspect in this case it actually means more like "not as close in alignment to the way things used to be, which I liked".
I'm fairly new here, and as a newbie, I haven't ever been taught what the existing community thinks I should upvote, whether in submissions or comments. Beyond the guidelines, which state:
> Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.[1]