Turns out, a lot of it, actually.
You might think that neuroscientists already have enough brains, but apparently not. Over 100 neuroscientists attending the recent annual meeting of the Society for Neuroscience (SFN), took part in an annotation challenge: modifying scientific papers to add simple references that automatically generate and attach Hypothesis annotations, filled with key related information. To sweeten the pot, our friends at Gigascience gave researchers who annotated their own papers their very own brain hats.
I suspect I’m missing some context, but taking a stab: the bots are hoping you’ll accept/approve their replies so that you put their links on your page for future clicks as well as SEO purposes. Like most spam operations, they just need an ~2% response rate to make the few cents that make doing this worthwhile. I personally blacklist some of the worst offenders by domain name, IP address, or judicious keywords.