I can say 100% that 60% of all bounty is a Scam. The reward for them is either given and the tokens will lie on your wallet forever or do not give at all. Then what's the point of doing this ?
The point of doing this is - like you said 60% is a scam projects but then we need to hit these 40% , legit bounties. i participate in some bounties that turned out to be a scam, wasted so much time, but i will keep doing bounties. I hope that Ico will ever be limited and scammers will be harder to get the victims.