If I must say the reason is no far from their current situation, check most of those coins that get a sharp pump drastically dropped few hours after the boom, if you talk about more stable coin movement then we can be sure of some little stability in their price growth and moving inline with other coins such as bitcoin so as the general cryptocurrency market make sharp market uptrend movement so will other altcoins who have usercase will increase.
-But any coin that have it's own parallel market pump will drop as sharp as the team cash out their gains.