if IEO could give big profits percentages to investors , maybe ICO slowly will lefted by investors.ico could not give any guarantee when they will listing in exchanges.investors need certainity about it cause they want to moved into another projects that maybe will give them profits too.
as long as there are potential and good ICOs, they will not disappear. now maybe the one that gets crowded and gets the trust of investors is the IEO, but if we also see not all IEOs get good responses from investors. all are limited to the IEO which is done in exchange for big names.