Why do people say daddy during sex?

Samantha • 23 Years old. 💏 Partner of 12 years.🤰🏻 with 👶🏻 #1 💕

My partner and I are always up for different things in the bedroom but he's a firm HELLLLLL NO on the subject. What do people get out of it? Is it worth a go or is it a strange as it seems at face value?