My reason why some ICOs often fail, it's all possible projects that become the person who handles and promotes the token also fail, because the project idea itself. The idea of a bad project has little chance of success. Most developers also fail to notice cryptoeconomics or token demand and inflation is a big factor.
I also believe that at this time, the main problem with ICO in the absence of fresh ideas. Last year there were many promising ICO with fresh ideas and some innovation. This year, all ideas have to repeat itself, therefore they attract less attention from potential investors.