Reddit, very famously, used bot traffic at its inception to create the illusion of a community big enough to compete with Digg.
It was the OG "fake it till you make it" business.
As the company implements an increasingly draconian "ban every account that looks at me sideways" admin policy, I'm not sure if "2/3rds of the traiffc" isn't lowballing it. There are entire threads - from initial post to bullshit bottom comment - that get created by bot traffic on the modern site. It's a full blown hall of mirrors over there.