What is the appeal to a Daddy kink?

I try and be very open minded and live life as "as long as you're not hurting anyone do what you want" but I really struggle with the daddy kink thing. I don't understand how it's a turn on to treat the person you're having sex with as your father figure. If it's about the power dynamics why not use sir, mister, even master. Why does it have to be "daddy"?