How come a lot of people don’t have many friends?

My older brother told me I’d be surprised how many “true” friends people have. My siblings and my late father kept reminding me that “Not everyone is my friend and I’m the kid of person that would be friends with EVERYONE and I’m easily manipulated and I need to read people.”
My dad criticized me for not reading properly, and that’s what always gets me in trouble and I am naïve. and then later admitted that he doesn’t see the person’s true color. Hypocrite. I only have 1 friend. My brother only has 3 friends and my sister has 4.