The most obvious reason why every Duke and Harry can run an IEO on P2PB2B is that they have free listing opportunities for projects. The project only needs to meet with some conditions which are not stringent. Some projects use  both P2PB2B and other exchange for their tokensales and that's a bit understandable, but for those projects that use only P2PB2B for tokensales, I advise you don't waste your funds.