[1]Why are there so many scam bounties out there and [2]how are we to know which is scam or not
[1] Because there are many newbies that can easily be scammed by these scammers.
[2] Its difficult to know which are the scam and not but here are some of clues. If the project is cloud mining and lending platform thats an obvious scam.
True, at most cases they are scam, like Bitconnect and all its copies.
But there were some legit lending projects like MoneyToken, ETHLend or Fintrux.