Cookiecaretaker explained it nice and short, but.... yes, that's exactly what hey do. Things are not happening in their real life, regarding women having zoo sex, even if these guys are not single. So, the next step that's very close to writing a story, but gets more social interaction is faking being a woman. Then, they can state some sexual exaggerations as truths, even though some women may have that much zoo sex in real life. They also hope to be able to talk to more real women or couples, usually.
I used to fake as a bi woman over 20 years ago in chat rooms, but I started to be able to sniff out other fakes. That frustrated me so much that I quit faking too. I hated it done to me, so I saw the gravity of faking towards other people.
It is very prevalent on zoo forums. Of the active female accounts here that post a good bit, I bet 2 in 3 that post mostly to explicit threads are fake.
I bet 33% + of visitors to the site actually are women, but so many stay silent or rarely post for multiple reasons.
I think the poll asking what's between your legs currently says that about 24% visiting here have a vagina.
I chose an androgynous name here not in an effort to get close to faking, but because I like the French male use of the name Renee, and I'm also a bit androgynous at heart.