I'm not defending them, but I think I can explain their intentions.
I've done it before, years ago. I made a fake profile, claiming I was really big. Obviously some believed me, most didn't. Those who did messaged me, and we chatted a bit about situations, and how interested they were in it.
I've posted before about how obsessed I am, and how badly I wish I was utterly massive. I'm average (6.6" inches long, 5 inches around) which is fine, I've never had a girl complain about my size, and I seem to do a good job at pleasuring them. But for some reason, I really do wish that I had the biggest penis in the world.
That profile gave me a medium, one where I thought I was the only person to think of "faking" my size. I acted, then realized it happens often. But I still had fun with the people who believed me. Hell, they might not have believed me, but went along with the fantasy regardless.
Something that would turn me on more than anything in the world is someone referring to my penis as large. Reactions are so fascinating, and amazing, that even though I've never had any type of reaction like that to my penis, it turns me on seeing OTHER people's reactions to OTHER penises, as I pretend that it's my penis they are reacting to.
I know I have to accept who I am, and will probably never be as big as I'd fantasize, but when my fantasy involved interaction like that, what other choice do I really have to dwell into it?
Roleplay isn't good enough, because I know the other person knows It's just a fantasy. But if from the start, the person seems to really believe I am what I am lying about, it's much more interesting that way.
Again, I haven't done it on this site in...like...years. I was like, 16, and I've gone beyond lying like that, but I still crave that kind of attention.