It's not necessarily that people thinking 20% interest is safe is greedy. It's that many people don't have the financial literacy to understand that something paying that high of an interest rate is going to be risky. And that if someone 'guarantees' an interest rate of 20% then it's probably a con.

So many people just lack the basic literacy to recognize when something sounds too good to be true. And in the crypto market it's worse than that, because all of the memes and in-group behavior functions to drown out warranted skepticism.