They should be prohibited from engaging in any activities related to cryptocurrency..
You mean stopping them; they will only do that if caught. In a physical world, there are syndicates and gangs, and so we also have that on the internet. They are well organized, and they have diverse talents and skills bonded together to steal people's money because there is a lot of money to steal on the internet because of newbies who do not know how to handle security and are easily deceived by these fake and phishing sites.
And they will continue to exist as long as people do not take security and education about these scam investment sites.