There've been a lot of good answers already, but I would like to add that some people just aren't demonstrative generally. I'm not. I know that doesn't really answer your question re: disdain, but I think it's worth bearing in mind that people have different attachment styles and habits, and so their baseline level of connection to the therapist will look different.

Another thing worth bearing in mind is that the therapist is (for some) a fairly safe person to hate.For those unaccustomed to allowing themselves to feel negative emotions, the therapist makes a convenient and safe target.

Sometimes therapists absolutely deserve the hate clients feel toward them, and the clients stay for any number of reasons.

This is a fine question to ask, I think. I don't always understand what I read here, either. I'm glad you're seeking to understand rather than jumping right to offense.