The algorithm aggressively promotes freshness (things posted in the past few hours for certain queries!) and 10+ minute long videos.
Every algorithm change directly impacts what creators, create, because no one wants to put in a whole lot of work for something to never be seen.
If, for example, the ideal format for a joke or video is 3 minutes, that either gets disappeared from public view or becomes part of a longer video.
The real answer, in my opinion, is that current recommendation engines prioritize profit rather than quality or innovation. Or perhaps their evaluation metrics are so bad that their goal is misunderstood. Or perhaps those who stand to profit have become too adept at gaming algorithms (or human psychology e.g. lewd thumbnails) that they degrade results.
...or perhaps we all suffer from nostalgia and forget how terrible the results were of yesteryear.
Who knows, all I know is I feel disappointed in what the internet has become. Even this thread is really just an ad, hijacking our biases and climbing the HN ranks accordingly.