Because greed let people keep on waiting for higher and higher value for there coins and end up selling at dip.
Since price can’t go up all the time.
I don't believe that greed is the problem. Didn't Warren Buffett once said that it is wise for investors to be “fearful when others are greedy, and Greedy when others are fearful.” So at a point in your Investment life, you have to be greedy to be able to make good of your investments but the problem for me in this regard is Investors lacking an understanding of the market. So, when you understand when to be Greedy and enter the market hard and also when to pull out, you wouldn't have any problem but when you lack the necessary knowledge of the market, then it comes off as Greed but it is actually the lack of market knowledge.