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?
There was a time in this market in which people invested in a project because they believed in the project and that is why they held their coins, they mined some of it and those that could found bugs and improved the wallet and the coin itself, those days are over, people want to obtain profits, it is that simple, and they are not going to hold their coins waiting for the price to recover, they will sell and get their profits and if they can buy at a cheaper price in the future they will do it only if they believe there is a possibility to make some money.