Bots aren't just search engines.
A lot of bots are marketing, spam and hacking bots also.
Just to give you and idea of traffic that is attributed to bots, last week I did an analysis on my 4 sites I run, I could identify atleast 50-60% as some kind of bot (search,marketing,spam or hacking), and probably if I looked in more detail, I would say I would find another 30%.
It's a bit disheartening that so much traffic is not human, and is just mostly 'noise'. :(