Banned users always just make alt-accounts anyway. Not really sure we'd see as much of an uptick in conversation and activity. The issue of traffic has much more to do with a decline in parity of the console wars, the fact that this site originated pre-facebook, instagram, etc, and the reliance of modern websites on mobile, which this site lacks almost completely. Good luck if you ever get logged out on your mobile device. It's almost impossible to log back in because of the wonky interface.
It's not pre-Facebook (which actually originated in '04 :P), but your point remains.