Competition is in PLY (play money currency), but rewards are real BTC. You do not have to deposit to win BTC, but people still are not interested.
any explanation why they are not interested?
Okay, person signs up... doesn't see anyone on... leaves. It's as simple as that, I'm not sure if there's any easy way to combat this but to tell people to invite their friends to play with them then others should come.
Thats why I suggest freerolls. So players can play and see how your app. works, and those who have won can cashout and tell others that your website is not scam.