Why are people so judgemental as to if you dont get along with your family?

To be frank, if you find 100 people who have a good relationship with your family and 100 people who don't, the former is going to be a lot more friendly, healthy, and well-adjusted than the latter 100 on average. Both groups will have lots of good and decent people in them and often, you just get shit luck in the family department. But the human brain is built to recognize patterns and it's not always going to be super fair about it.