I have purchased CS:Go directly from steam using bitcoin yesterday so i am quite sure you are wrong about steam still doesn't accept bitcoin for buy/sell of games. They are accepting bitcoin payments from few months ago using bitpay as third party bitcoin payment processor.

Talking about games that reward in bitcoin for playing or host competition and pays users in bitcoin, there are not any big platform just few faucet based and flappy bird like games are available in play store which pay really small amount just like faucets for playing games.