in my experiences, they dumped it because of panic. i have joined some bounty in the past, some project give a big bonuses for investors. when they get listed on the market and start to trade, the bounty hunters still didn't get theirs reward yet. the team still hold it and let the investors sell it first. then, the investors sell their bonuses first and hold the rest of their coins or token that they've bought for later. when the price is little dumped, the reward was distributed to bounty hunters. they all panic. they think the price will get more dumped and sold it immediately after distribution. then, it just make it worst. the price is dumped really hard.