Maybe theiy need funds to support the daily budget.many reason why people sell bitcoin.number one reson is need money.
Yes, there are a lot of reasons why people sell Bitcoins; obviously they want to have their profit as soon as possible, the other one is, they don't trust the security of their wallet to protect their Bitcoins so they don't hold it longer even if they want too. Furthermore, they have daily needs so they really want money.
In short, they are not fully committed in bitcoin so they are scared and they keep on doubting in bitcoin because they think that having bitcoin is just risky because of the chance to lose some money because of the price volatility. The security of the wallets are not that big deal because they can make it secure if they will just do the security recommendations.