Not all people sell altcoins soon. Some are instant moneymakers. They dont have patience to wait until the price gets moon and sell at lower profit. Trading on cryptos something like taking a risk, bigger the risk, bigger the profit or bigger the loss.
Loss and win are usually the result in any investment. It seems some people are getting to risk their holdings while waiting for such a good price. Waiting for so long without any assurance of having improvement is totally a waste of time, it is better to sell and go for other coins.