I think part of it is the content isn't particularly useful for a bot to act on (not pushing products, not a lot of politics, etc). Another could b the audience is tech savvy, so they're less likely to fall for bot stuff and more likely to report it. Then the moderation is higher quality than many other sites. Finally, the overall population here is low, so it's a smaller target.

That said, I do occasionally wonder if certain of the comments are from real people. Although an occasional comment from me could have others thinking the same.