WHY?

obviously, a lot of questions begin with this simple statement. but what I really want to know is this: why must commenters leave a full account of their experiences on a blog in lieu of commenting on the post or to other comments that have been posted? the most common of these seems to happen when someone posts something about pain/pain medications, so instead of reading comments pertaining to the post itself, I am reading comments detailing full experiences in the er/surgery/hospital stay/personal experiences with certain medications. Not that I mind, I just want to know why people do this?