Actually You Don't Get it!
They Distributes airdrops or bounties Reward their own currencies or Erc-20 tokens!
Which Don't Have value yet or have a Low value which can increase or Decrease Significantly!
Thay way, they saves loads of money!
Now if you want your rewards to be Valued then you have to select those Those Projects Carefully and smartly!
More Promising Projects means More Value!
If you're working hard for some crazy project then Choose them Wisely!
So how much someone can earn from this?You May read
This article from Wired Bounty0x Hunter “Crypto Shaolin” (a Virtual Name) Says Wired She earned 50,000$ From Bounties This were!
Read the article Above!!