It's rather because your average person (maybe not your average HN reader) browses the web with a single window filling the entire screen. If paragraphs did not

It's rather because your average person (maybe not your average HN reader) browses the web with a single window filling the entire screen. If paragraphs did not wrap, you could end up with lines 2 feet long which require you to turn your head from side to side as you read. An open newspaper may be 3 feet across but they put the text into narrow columns for a reason. If you want to jam in more ads, the real shithead trick is to split the story/article across multiple pages, so you get multiple page-loads per story.