There must be a time when new innovations will replace the old system. Like ICO, it is replaced by the IEO because each system has a negative and positive side.
There will be someone who will replace the IEO in the future, just need to wait.
There is always an update in everything, ICO to IEO, maybe they were not in the same person idea but it's the first product or event concept that just adds some better option that can contribute into that product success. It's much better in ICO since it is offered already in exchanges that gives confidence to investors.