When a person goes in for counseling due to emotional problems, why don't the counselors include other family members as part of the treatment?

I have a feeling that most people who receive counseling due to emotional issues are in complete denial of how their behavior affects others, especially their children. Their children, in turn, have emotional issues because of the dysfunctional way in which they’re raised, but the dysfunctional parent doesn’t see their behavior as dysfunctional. If the kid develops problems, it’s all the kid’s own fault.
I ran into an acquaintance yesterday who told me her 3 year old son got kicked out of daycare due to his behavior. They were removed from a doctor’s waiting room for the same reason. She swears she doesn’t understand it, he’s just doing “regular 2 and 3 year old stuff.”
He is not just doing regular 2 and 3 year old stuff but apparently she can’t see that, and above all, she can’t see how her behavior is contributing to it. She dangles bright, shiny things in front of him, and when he reaches for them she snatches them away snarling ”NO!!!!!!!!!!!!!!!” ...for no reason other than to prove she’s the boss. She thinks that is normal parenting. Can you imagine the frustration levels the child must experience?
She is in counseling, but how is the counselor supposed to know about these types of problems in her relationships when the patient doesn’t see them as a problem?

So why aren’t other family members included in the counseling? Or at least people with a different POV?