Maybe since they thought that the pump will continue for some more time, so even if they buy at that pump time, they can still gain profits for a bit, although not as much as when they buy it in the low price. However it's surely kinda risky though, since when the coin is pumping already, the chance that it'll go down will surely be high, when the coin is expensive, of course lots of people want to sell it and gain profits, thus the price will decline. but not many will understand it, or maybe they just like to take the risk. But I agree that FOMO is really scary sometimes. You can experience lots of loss because of that.