I think that the biggest dumpers are teams of ICOs. They raise money from token sale, but that is not enough, they want to sell their tokens (30-50% from all existing tokens). WHile bounty hunters have only 2-3% from the total supply. So how can they cause a dump?
Yes, you are right. The main reason for the price drop is from their team. They even extend the time token sales with a bonus of 50%. I wonder. Why are they so enthusiastic to sell out their tokens at such a big discount. In fact, after that, they can not be listed on big exchanges.