I've seen lot's of people who complain to bounty hunters who dump their tokens after they get them. Why hate them? They have all the rights to sell whenever they want and bounty allocations are only 1%-5% of the total supply of the coin. I don't think it will do much to lower the price of the coin. I mean it's even good for the ICO investors as they will have a chance to buy more tokens with lesser price than the ICO.
Holding the tokens also doesn't mean it will make you rich. Some tokens get abandon by the developers so it would be better to sell at a good price than be left hanging in the end.
Simply becasue they don't see any benefit of holding it for a long time and they are also afraid that their token will be valueless since a new altcoin has to surpassed a lot of challenge before it gets in top coins in coinmarketcap. Another reason is also the need of using the money. Bounty hunters most likely are not rich; thus they need to secure their needs and wants and selling as their coins as early as possible is the best solution for them.