Why don't I like being affectionate with my parents?

My mother asks me to sit with her in the living room almost every day. And I do love my mom and respect her and I dont mind being with her. But I dont like my parents touching me much and I get irritated when my parents show affection towards me. I also get really irritated when she starts asking meto spen time with her. I dont like being affecionate with them either. I dont know if its just my parents, I think it would also be the same with the rest of my family, but I dont know them because they're in another country. It doesnt bother me at all either that I get angry or hat I dont like being affectionate, I just want to know why that happens. I dont mind it from my closest friends at all. I dont like being touched by strangers or my parents. Why does this happen?