There are also QR codes for special Miis and DLC for certain games, like costumes or levels, but those are mostly user generated.
To my knowledge, there is no way to encode an entire game to a QR code, and even if they did, then it would be marketing suicide because most people do not know how to use QR codes, and anyone could post a picture of it and make it a free game (unless they included a one-time usage feature, which would defeat the whole purpose of making a QR code in the first place).
Why Are people so obsessed about free games... You dont get free games At GAMESTOP/EBGAMES SO WHY EXPECT IT ON THE ESHOP!! GEEZ BUY YOUR OWN GAMES LIKE YOU DO AT EBGAMES/GAMESTOP
Well, I geuss because of the mobile market. You see, with mobile devices blowing showing themself as portable gaming devices some poeple got different ideas about gaming. Keep in mind that most of those game are free to begin with and have add-support. However, people seem to forget that last bit and expect it wider-ranged on more devices.