Different levels of power is unavoidable. It is part of existence. Those differences may balance out when dealing with two individuals, or groups, but typically there is a more powerful and a less powerful.
And typically the more powerful group takes advantage of the situation. That’s long been advantageous but the advantage has also long become a hindrance on real progress. A parasitic replacement for it.
It doesn’t take humans for this to arise, but humans have spent millennia institutionalizing it in numerous forms.
“How to stop being animals” is too flippant, and not terribly accurate.
Regardless, our society and history is so permeated with this concept / construct, and with attempts to enshrine it as unshakeable truth of being, that “doing something different” is incredibly difficult. For many reasons.
It is so pervasive that it is borderline… fractal? The power structures showing institutionalized abuse are parts of power structures that… abuse of power differences all the way down.
More angles for explaining why than you can shake a stick at. Not a lot of broad “why not,” it is usually focused on some localized example.
That’s an attempt at describing it.
From that point of view the best 'solution' would be to spread power as wide as possible. I think in reality the reason power hierarchies are useful is because spreading power too wide leads to Ochlocracy.
In the same way democracy is good or bad depending on the level of rationality, morality in your population; but for modern society I would say it's mostly bad (e.g. if you let the average man on the street 'solve' climate change he would lay the foundation for a dystopia)