Could stadia get a petition or something for games the players want instead of each player contacting the developer. That way stadia can bring there petition/poles to Activision and other gaming companies and show how many people are eager to play there games. I just don't think many people will end up taking the time out of there day to message them but if it were a simple pole it'd be a lot fast and simpler.
@DaniGamePlayer made a really nice form that is kind of what you're asking. It's not a petition though, but more a form as an indicator of which games are mostly wished by the community. Here is the original post. The form can be found there, but you can also click this link.