Why does her dad hate her?

My best friend's family are really well off and have a big house and loads of money tbf. Anyway, a few days ago me , my friend and her brother went out shopping becuase her dad made us go with her brother. When we was out her brother Luke was having a go and in the end he punched her twice. My mom came to pick me up, and their dad got them - but my friend got all the blame? She told her mom and her mom stuck up for her in an argument with her dad erlier. Anyway he dad all of a sudden started calling her a spoilt little ***** and any other name he could think off (just like his son had done a few days ago) and i cant understand becuase its HIM that spoils both ofthem not the mom? He stuck up for Luke but not for my friend. Its fathers day so why is he being a nob?