Google has announced its new policy along with its latest "bad ads" report, where it has revealed that it took down over 3.2 billion ads that violated its policies in 2017. It didn't explain its reasoning behind the decision, and only said that it "updated several policies to address ads in unregulated or speculative financial products." In addition to cryptocurrency, those products include binary options, foreign exchange markets and contracts for difference (or CFDs).
ICOs blew up in popularity when cryptocurrency values soared over the past year. It came to the point that South Korea and China had to ban the unregulated means to raise company funds by selling digital coins. Authorities around the globe are cracking down on ICOs, since they can easily be used to scam investors. Unscrupulous individuals could launch coin offerings with the intention of selling products and services that don't exist and will never materialize.
In the US, the Securities and Exchange Commission warned celebs that they must disclose if they're promoting a virtual token or coin. More recently, it sent out subpoenas left in an effort to extract info, such as the structure for sales and pre-sales of the ICOs, from companies in the cryptocurrency industry. SEC chairman Jay Clayton said outright that many ICOs are "being conducted illegally," and Google likely wanted no part in their growth.