You should Private Message one of the DEVs, like Frogsquadron, and ask. During one of their surveys they asked for companies that, we, the players would think as good fits for the G2G platform, as it is intended to be a co-creation platform. However, as to the reason why there are no other games, I think it has to do with the fact that G2G is technically still in beta, and it's probably difficult to reach out to other companies and get them to use this (+ it would probably be a logistical nightmare). 

Also, the co-creation part of G2G is for the players to co-create with the developers. 

For now, I would say creating a thread in the Off topic, Creation, or General (though that's generally reserved for Amplitude/Endless related topics) in regards to your game idea.