Because they believe that Facebook prohibits bitcoin and ICos and other cryptocurrency
The new Facebook policy will not allow announcements of known digital currency exchanges or initial offers of currencies.
Is it to avoid fraud or false advertising? That's why?
It is not against cryptocurrency but it is preventing the increase scamming schemes via cryptocurrency related projects that utilizes facebook's cheap and easy to access advertisement in which if this will not be regulated then it will also affect the credibility of facebook itself.