They are mostly paid, so do not pay attention to ratings. In general all rating websites are paid, so you can create whatever rating you wish, if you have enough money. Do your own research and do not trust such websites.
Probably, because some of the ICOs project having a good ratings till failed. There are many factors why a project failed, according to study I read, almost 80% of projects failed. When value suddenly drops means there is someone dump their holding, and what happens next is domino effect until it cannot recover or developer abandon the project.