Now the story has changed as it only serious projects that would want to go through IEO's, we no longer would hold only the project body responsible for any IEO scam but the exchange, so any exchange that values its reputation and users should do a proper scrutiny about any project before accepting their IEO sales. For instance if an exchange fails multiple times with their IEO, it will drive attention away from them, that is why Binance still draws a lot of attentions because it has recorded more successful and profitable IEO's.
The answer about Binance success in holding IEO is pretty obvious, they are the number one exchange and they don't want to tarnish their reputation, and they will continue to protect it because as long as they are accepting good projects, their platform will attract more investors and people will have high regards to their exchange, and they will continue to be a leader.