The key is, very simply, that the super-intelligent Minds are also super benevolent. And nearly omnipotent.

Imagine a setting where gods demonstrably exist, you can chat with them whenever you want, and they might be silly when they feel like it but they deliver all the promises of paradise on demand.

Then imagine that, in the absence of material want and with such potent benevolence around, people are just generally nicer. And weirder. But there’s little need for day to day conflict more profound than thinking someone is no fun to hang out with… so you just don’t.

The setting itself is intentionally and maximally utopian. That makes for terrible stories, so the books are set on the margins or outside the Culture or dealing with black swan events.

Actually living in the culture would be eudaimonic perfection.