On Twitch, "Followers" is a tracked and important metric for streamers (publishers). Therefore there's obviously a lot of benefit to buying fake bot followers and inflating your count.
However, sometimes misguided fans of streamers will buy bot followers for them intending to be helpful (or even to spam them with inappropriately named followers).
From Twitch.tv's perspective, tracking down who issued the bot followers is of paramount importance since they have an interest in preventing gaming of the system without catching innocent streamers in the crossfire.
Twitch actually maintains a help page on what to do when you're being spammed by followers, and it includes a statement that they won't punish people who haven't paid for spam. In my experience, whatever mechanisms they're using under the hood seem to be reasonably effective - I have yet to see someone incorrectly banned for this.