This is true. Famous exchanges like LAtoken went being a scam just because of bad IEOs.
Binance is much trusted and people hold BNB tokens in the exchange mostly because they want to be the first to buy the IEO token and investors blindly put their money on any IEO because they know they would get a profit. If binance started adopting any IEO, not only people would not trust the platform, it's BNB holding strategy would also backfire making it's token valueless.