The fact that being IEO does not guarantee the success of the project. IEO is just a method or strategy adopted to perform the token sales of a project. IEO has surpassed ICO because it has a well-structured way of issuing the tokens via the exchange. Here, the tokens have higher probability of getting listed on the same exchange after the IEO ends, hence investors are assured of trading right after the token sale and will not have to wait for the long period full of promises on when to get the coin listed as some ICOs do.
yeah like my statement above, even some project are launch IEO project, this is not guarante the project are successfull deliver the product after IEO ended and raised much money, because this is just another method from developer to raised more money from investor by partnership with exchanger.