That means you are buying bad coins, so there is no demand after the main exchange list. Actually the value of the coin falls there are several factors that affect it, such as:
There is no demand, investors sell at any price.
Too many bonuses
The most important thing for me to sell altcoin is more than the price you buy. that's the principle I use!
many holders are also not interested when the coins only enter a small exchange, investors will not think long to throw away their bags, the betting program after the ICO period is also still boasting empty so far, the number of coins has indeed increased but the value has decreased badly.
if indeed the reality has never touched the ICO price, I usually detect by trading it, the right time to sell is when dev always issues wise words that have no meaning, while prices go down uncontrollably.