Pretty well summed up by other comments, but loss of ROI. Funny enough one of my last blog posts was the most response I've ever gotten (few hundred K readers, tweeted by O'Reilly, liked by Zuck) but it still felt "not worth it" in the end.

Now blogs are simply the place I put something if I truly write something for enjoyment where that enjoyment needs to be 100% of the reward. This does happen, but rather uncommonly (because: life).