Those people who sell bitcoin when the price is low will have some percentage of benefit because no one wants to lose their money so when they buy the Bitcoin may be at that time the price was lower than the price of selling so we don't know about the other person that why he does so.
Also individuals that sell at lower prices may have not enough knowledge of holding or maybe they are afraid of Losing more money than this. It is necessary to hold your bitcoin for at least 5 to 6 years after that if in bull run you want to sell it then it will be profitable for you.