Because the teams of these projects hold different events to interest investors and raise the price of their coin. That is why the price of their coins after listing does not fall, but begins to grow.
The market moves under the influence of supply and demand. In whatever events the team did not participate, the price will fall if no one wants to buy. I have examples.
I agree that the product must be usefull for people. The more people use the product the higher is the price of the token.