Take a look at https://stackexchange.com/sites, does every user in stackoverflow.com visit the site 3 times a day? Or is the anonymous traffic just huge? (for every site in stackexchange.com, by the way)
1 Answer
For most larger SE sites, more than 90% of traffic is from search engines, those users usually don't have an account on the SE site. I don't see anything unusal with these statistics.