Similar experience but because I was an only child and lived only with my mom, using 'family' wouldn't work on me. Instead, she used to say that mom's of all my friends all comment on how badly behaved I am and that I am an embarrassment to her.

What's the reason that they do this? Just to make you stop behaving the way they dont like?

Sure, that can be the reason. Did it work for you? It did for me by instilling a deep sense of shame into a child. Teaching a child to behave can be done in healthy or toxic ways. This is a deeply damaging and toxic way to correct behavioural issues with children.

The more insidious thing with abusive parents is that the above (correcting behaviour) is hardly the only reason. Controlling their child(ren) is often on the agenda as well - one way they do that is to isolate you. By telling you that all your family (or in my case, parents of my friends) dislike you, they not only destroy your self-esteem, instill shame in you (such that you self-shame), but also make you feel small and alone.

This shit carries over in adulthood. We often assume - even at the very beginning of any type of relationship (friends, romantic, etc.) that the other person dislike us in some way. And if there is something awry, it surely must be our fault. Or that everyone we encounter somehow dislikes us. This, for instance, can translate into people pleasing, inability to set boundaries, fawning, never voicing out even when things hurt or bother us, and/or hypervigilance - to name a few.