If you look at product reviews, people are more likely to write a comment if they have an issue with the product than if they don't. I'm not sure how much this

If you look at product reviews, people are more likely to write a comment if they have an issue with the product than if they don't. I'm not sure how much this applies to github topics but it could possibly provide it's own bias towards negative comments. Also, as others have mentioned, it only takes one person to write a negative comment, then others could +1 that.