Wayne's charity works are already global. If he makes some sort of overt connection to--for all intents and purposes--a foreign government, people will look into it. It also raises the question of why he never did something like that before. It also creates a connection between Batman and the Amazons and Bruce and the Amazons. That's not to say he wouldn't entertain the idea if he weren't dating Diana, but again, the scrutiny would be something he'd want to avoid.