Following Facebook, Google also decided to forbid advertisement of cryptocurrency as its policy change.
The Guardian: Google bans bitcoin adverts in cryptocurrency crackdown
Google explained the policy as for improving ads experience across the web with removing harmful or intrusive ads.
Indeed, there are many fraud cases using ICO reported recently. The Japan government published the policy to prohibit citizens from participating foreign ICOs recently. If a customer is tricked through an advertisement on Google, Google might be sued for supporting illegal activities. I understand that Google is concerned about the risk since advertisement is still the main source of income for Google.
On the other hand, Google prohibits not only any advertisement of ICO but also those of cryptocurrency exchanges and wallets. This inclusive prohibition policy looks excessive. Cryptocurrency itself is an innovation in modern IT industry. If Google does not commit it at all, it will be left behind the modern era. What is expected for Google to judge the quality of service any advertisements suggest.