I think most of the people here have the same reasons why dumping, because it costs money or because the token doesn't have much progress (it has a small volume and doesn't have any updates)
When people are seeing the project didn't have a lot of potentials and then they will be dumping their tokens to the market. Their decision will be affected by the progress that has already made by the team and how good the product that has already released.
This is what I think and do! People usually invest in a project with the expectation that the project has a huge potential to pump. However, after some period of time, they may realize that the project can't pump and even dump, they'll sell the tokens. That's what investors do and it's a common behavior in the business. We sell anything that doesn't have the potential to get back the money!