It's much easier than you can imagine - it's one of two ways to get the token without investments and without investing money in them. So simple
you cannot say that doing bounty can be done without investment because we are actually investing our time on it . some people do also invest thier money to buy forum accounts and social media accounts because they wanted to earn more profit than usual . there were also people that is paying other user just to pilot his accounts because he is busy on some more important events . see ? even bounty also needs capital or invvestment in order to make it more effecient and effective .