Why are most parents against sleepovers? Also why are they so brutally honest about their kids?

My late dad NEVER allowed sleepovers or let me go to sleepovers unless it’s at my cousins house or my best friend. Even my siblings and their spouses don’t let their kids go to sleepovers accept family members.
I wanted to go to this popular girls’ birthday party and sleepover but my dad said NO. He said I only knew her for a couple months, he didn’t know what kind of people their parents are and unless he was there, I’m not going and that’s final. He asked did she ACTUALLY invite me to go or did she just say I can come if I want just to make me happy. Wow…..that was harsh. I would get angry at him for not letting me go but he didn’t care if I was angry. He didn’t let my older siblings go either unless it’s their best friends or family members. Even if it’s a friend of theirs or best friend, parents still say no to sleepovers.