A lot of people don't want to be taken care of. They want to take care of themselves.
Perhaps they had bad experiences as children with the adults in their lives. I know I certainly did. Last thing in the world I would've wanted was adults looking after me. They were incompetent, they had no clue. I was safer without them. Maybe they're like that.
So that their relationships sometimes contain a distance. An empty place where there's a deliberate lack of intimacy.
They compartmentalize. They keep their troubles to themselves, to some extent they keep their joys to themselves. They share the parts of themselves that feel safe to share.
Sometimes, that's merely sex.
They need the sex. We're mammals. And they want a certain controlled emotional intimacy.
It's not that they just want to fuck-and-run. They actually do want the relationship. But it's a guarded relationship which is awkwardly constrained.
They can't talk about what's important to them. It's important to them to not talk about that.
So you think you know them, but you don't know them, and you think you understand their needs but you don't understand their needs, and you think you know how to relate but you don't know shit about relating.
The rest is obvious.