Because he asked what he could do to improve the reception of his comments, and was told that a major problem was that he spread random ideas across dozens of comments, cluttering threads up, and then proceeded to follow that advice. (Or, in more Less-Wrongian terms, he updated his beliefs, or something.)

People are showing their appreciation for the fact that he listened. Doing so is a great positive reinforcement of community norms, and makes users happy to follow the norms as they get rewarded for doing so, as opposed to the opposing strategy of downvoting deviations from the norm, which might result in resentment, as they would experience only punishment.