I am sure it has been suggested before but one more time wont hurt anyone.You say people play scenarios and noone plays 3v3 and thersnot much competition from new players.Well thats also AWs fault.
-Make standard map europe + extra cities so that people without premium can host it.Until this is done only a very small percentage will join these games when they reach rank 6 and up.
I talked with people that i ranked up with about the reason so few of them play 3v3.The main reason is that no games except the very competitive ones are being hosted and they are not familiar with the map.