Perhaps because you're posting answers to old questions that are (1) six months old and (2) have already been answered. You're not adding any new information, you're just posting. It gives the appearance that you're just trying to accumulate PGC points. If you want to leave a comment, feel free -- no one can downvote a comment. But when you post something as an "answer," it means you are attempting to actually answer the question asked.
Look at it this way: if the question was already answered in great detail six months ago or more, and then you come along now and say the same thing, how is that helpful to the original poster?
Or in this case, you're not even answering the question, you're just commenting.
Anyway -- those are some possible reasons. I didn't downvote you, so I'm just speculating.