The major causes after successful ICO is because of the investors that are invest huge amount during the pre sale and during ICO. After they have make their money and profit they have in focus they decided to dumped the token.
Discounts are evil. Bounty in tokens is evil as well. Both of them lead to a strong dump after the listing at any exchange. To prevent it founders should spend a lot of money to buy back tokens at the exchange with a high price. But there are too few teams which are able to do that.