Well there are lot of reasons why people sell bitcoins. People might sell bitcoins when they need money and selling bitcoins is their only way to get such money. Like me, I am selling bitcoins when I need money for my family. People also sell bitcoins because they wanted to have a realistic money than digital money because they are scared to the fluctuating price of that currency. Some are scared to hold their bitcoins because it is prone to hackers so once they earn it, they sell it already. People have many reasons why they sell bitcoins but it is not big deal because we have an individual decisions so whatever we did, we should not compare it to others.