in my own opinion why price down after listing in exchanges its because investors wants immediate profit and then buy back at lower price, hold the coin for atleast month till the price recover.
If investors do as like you said, "sell immediately and buy back at a lower price" this indicates that investors high optimism about the future of the project. this is a good sign ....
So why do we have to hold the coins till the prices recover?
wouldn't it be more profitable if we implemented the same strategy?