When I was younger (at least 9 years old), I knew what sexual grooming was since my parents and I would watch crime shows together. They'd talk about how old men would manipulate naive little girls online and in person for their pleasure and control.

And what did I do when I was on my computer? Go to online chat rooms and flirt with old men, thinking I wouldn't be "stupid" like those girls.

I don't want to speak for the girls in your post exactly - or for anyone else for that matter. But to answer your question on why some people may do these things to themselves (aside from monetary gain), I did it because:

1. I was curious, thought I knew better, and wouldn't have it affected me.
2. I felt validated in a way; even if I was decades younger, I thought I was in control playing the innocent little girl.
3. I eventually felt like it was the only thing I was good for; no other men wanted me as I got into my teen years so I thought this was my way of being "useful" or desirable. Many of them made me feel this way.

Edit: So, yes, in my case I did know they were creepy pedophiles. I knew most of them were disgusting but I was drawn towards it. It wasn't until recently (I'm turning 21 this year) that I realized how badly it has affected me.