Thank you for the thoughtful reply.
You're right, I didn't watch the videos. Not because I wasn't interested, but because my time and mobile data are both very limited. I was responding to the written post itself.
To answer your question directly, I think the main cause is the incentive structure.
The behaviors you mention: poor curation, nepotism, curation trails, whales not voting, rewarding friends over discovering new authors, etc., are real. Where we differ is that I see those as consequences rather than the root cause. People adapt to incentives. Economics tells us what behaviors are rewarded. Psychology tells us people gradually internalize those rewards. Someone who begins writing because they enjoy writing can eventually find themselves asking, "What is most likely to get rewarded?" instead of, "What do I actually want to write?" Once enough people make that shift, the overall quality of content begins to change. Usually to the detriment of quality. That's why I think changing the incentives changes the behavior.
I also don't think Hive or Blurt should be viewed as places where one expects to earn a living. I use both as permanent public records of my work while building opportunities elsewhere. Ironically, taking that approach ended up getting the attention of an editor who offered to pay me for articles at a rate far beyond what Hive has ever paid me. In hindsight, that has been a much healthier way for me to think about these platforms.
As for your point that your argument is developed further in the videos, that's fair. I simply haven't had the opportunity to watch them yet. If your position there is closer to what I've described above, then we may actually agree more than I initially thought.