Maybe Google is genuinely doing what they would consider a service—it's not like cryptocurrencies are the stablest of markets, and it's failed coins are piling up, along with indictments. Just like the government swooping in to save the day, Google could be doing that, too.
Or maybe Google is trying to hedge off Brave before it can get started. Nothing like good old fashioned gamesmanship to prevent a would be opponent from taking them out through advertising on its own platform, no less.
Or maybe Google doesn't want to support the decentralization of currency or whatever else potentially comes with it because it is in the back pocket of large, centralized government with its own fiat currency and economy.
Or, maybe, because it's an ad platform, it doesn't like the idea of an attention economy springing up, cutting out the middleman and hence their main revenue stream. It's not been that long since they essentially gutted every other form of advertising. Surely they wouldn't want the same to happen to them so soon.
They found out if you play blackjack in vegas you get free drinks and some tits in your face.
No free drinks/tits at the crypto tables. Yet....