Sorry for the delayed response. I had been quite busy. Actually there are services that are set up like google adwords and adsense. or like facebook ads. That are specifically for crypto based advertising that have a network where many websites run their ads.
My website. mykoscoin.com actually is part of a network called A-Ads. So Electroneum used Facebook because obviously due to the reach. They are after new people and want to bring people in. So facebook and google will reach more.
However, if crypto services keep building up their networks and websites. It may come a day where they can fully advertise just on crypto ad networks. So they have the foundation for it. It's several services like this. It's just because crypto is still new and has less than 1% of the world using it. You'll need to reach out to bigger networks in the early stages