The main reason of ICO investors are decreasing is due to lot of ICO are scam and even if the ICO is gone good they are taking lot of time to release the coin and list in the exchange. That is why it is better to buy in the market when the ICO coin is listed.
The scam is spreading and that really is what makes ico investors uncomfortable when they put a lot of money in and what they get is nothing, a very unfair bet, the win always lean on one side, and investors are not fools, there is no reason for them to stay and continue to lose. The era of ico seems to have lost its splendor, the project was not outstanding and the investors were not interested, it's a sad fact but I believe that until a certain time, the era of ico will revive, this is a way for the market to create a balance and create opportunities to make money for investors