There won't be any guarantee that locking token rewards for bounty will prevent dump in the market.
They think the investors invested on their project will never sell their coin, but they are wrong.
Some whales investors may want to sell some part of their token to invest in another better project they just found.
yes you are right and some investors don't care about prices on market. they will sell it without thinking of a loss because what they sell is only bonus they get when they are pre sale or ico