Because the N7 wasn't created with OTG in mind as a selling point. Thats why google doesn't market it. Otherwise google would have done something here without requiring root. OTG is a workaround that people are utilizing to do something that wasn't intended. Its a hack, a mod, however you want to label it. And with all hacks and mods, it requires the person to go that extra mile to do something that they could not otherwise do before.