People sell their cryptos just because they heard that a particular coin is better than the coin they have. To add to these, I believe dumping of crypto coins is also as a result of this kinda comparisons made by people.
A lot of people in crypto are to make a quick profit and they are not interested in understanding how it works and what is its future use or any other reasons. Their main aim is to make money and if that is not happening then they will start comparing with other coins which are either more stable or going up in that movement. I don't we can do anything for this segment of people.