Tried their JAV HD and couldn't convert them either.
I have come to the conclusion that people do not want to join a sophisticated porn site. It does not matter what it looks like, what matters is the content and how you sent them.
Also noticed that the "submits" count is pretty much useless, sometimes I have 100 submits per join, next week 20 submits per join, another program 3 submits per join, etc.. and similar overall conversions on each. I think hentai lovers just like to try getting in for free a lot.