I think that if the project is good and tokens are in demand investors will not sell the tokens. Investors will sell the tokens only if they do not sure in the project.
For some reason, it turns out that investors do not believe in the majority of projects. In this case, a strange situation: why buy these tokens? These are such "investors"? or do they constantly lose faith after buying tokens?

It works, when there only institutional investors who have invested in the project. If there are other token holders, like bounty hunters or private investors, they can sell tokens in any reason.
Someone has to sell due to circumstances, someone initially believed in the project, further became disillusioned with the teams activity and yes, most of the bounty hunters are not investors, for them this is a quick income.
Well, everybody wants a quick income, including investors. But, institutional investors do research projects activity, and they can predict the future price of its token. Bounty hunters can't. So usually, they sell token for any price.
Cryptocurrency industry are actively developing and investors want a quick profit. If they do not have a quick profit they are desapointed.