Nature doesn't have likes. Yes, there are various sorts of equilibria that are stable and other conditions that are unstable. And some forms of moderation that might be ideal are inherently unstable. But people still work to maintain moderation, and they would have done so 20,000 years ago as well.

Most extremes are themselves unstable and do not persist over the long-term. Winning big in the short-term does not correlate to long-term thriving. Cultures and species that have been dominant but then went extinct are numerous. Meanwhile, a lot of non-dominant forms of life have survived the eons.

The entire nature of life is a battle against extremes. We moderate in how much we eat, sleep, drink… Homeostasis is not a condition of being truly static and unchanging, it's a constant struggle against entropy. We constantly put in effort toward maintaining our moderation that defines a thriving life, and eventually we all fail and return to dust. Those of us who fall into extremes tend to lose our homeostasis sooner and return to dust faster.

I'm not saying that maintaining moderation is trivial. But the way most people live is through maintaining moderation via all the effort it takes to do that, to resist the pitfalls of the extremes. That includes getting support from others (e.g. therapists). If there's one thing we can say confidently about humans across the ages, it's that we are social and live in supportive groups that help each other.

It's not a matter of somehow just passively finding moderation. It's an active process, and we also don't do it alone.

What kind of people have you been interacting with that your impression of the non-depressed is "they think they own the world"?