I really think these IEO thing is only good for the top exchanges and these is because they have the liquidity and the traders to pump a coin after listing, which is why their IEO projects are usually successful.
But the smaller exchange don't have the same and their IEO success rate is no way near the top exchanges. Maybe 2 out of 10 IEOs conducted on the small exchanges would succeed, while top exchanges boast of a success rate of like 9 out of 10.
Hard work pays out, those bigger exchanges worked for it and if smaller exchanges wants to get to that stage, then they should work hard to create the hype that most of these exchanges has and has been using to make any of their project a successful one.
You are really not far from truth to say that the reason why IEO is successful on bigger exchanges is because most of them already have the volume that they will push to such exchange and because of their reputation, people tend to believe in them, but aside hype also, they still do their own due diligent to ensure that they continue to maintain their reputation by not allowing any project without real use case to be registered on their platform. This is one reason why they become successful.