Because YA is 50% trolls 30% dried up prudes and limp diks, 10% teens in their moms basement, and 10% people who actually are married and have a sex life.
The same reasons fake questions get posted all over the site. For attention; To see what kind of answers they get; Because they're bored and lack the creativity to find something else to do.
The one case that I know of here is bored and lonely. He got very upset when I pointed out to people that his stories were just that: works of fiction.
Pretty weird hobby, but to each his own, I suppose. I never fully understood why he got so indignant about it.
When I was single I did this all the time to keep the girl I was dating on the hook. To make her think she had a future with me, regardless of whether or not I actually really liked her. There are a lot of gullible women out there, and congrats, it sounds like you aren't one of them.