It's no secret that Google makes most of its money on advertising. Heck, some of our own ads are served through Google's networks. Due to the nature of the ad business, it behooves Google to accept as many advertisers as possible. Having said that, it's also important that the ad content Google is serving is trustworthy. That's likely the reason that come this June, Google will be banning advertisements for a range of financial products that includes all cryptocurrency-related offerings.
Specifically, Google is banning ads for "cryptocurrencies and related content, including but not limited to initial coin offerings, cryptocurrency exchanges, cryptocurrency wallets, and cryptocurrency trading advice." News of the ban comes from an update to Google's advertising policies, and the message offers no further justification or explanation for the change. It's possible that the company is concerned about folks getting fleeced and somehow holding Google responsible, or simply trying to maintain a standard of ad quality.
Other taboo topics covered by the announcement include binary options, contracts for difference, rolling spot forex, and financial spread betting. Advertisers may still be able to list advertisements for some of the products mentioned above as long as they licensed by the relevant financial services authorities in their respective regions. Google has a page that talks further about what advertisers of those products will need to do. There's no recourse for the crypto-coin crew, though—when the new policy goes into effect this June, they're banned from Google's advertising networks until further notice.