User blog comment:Kirkburn/Technical Update: August 31, 2016/@comment-896291-20160902185433/@comment-5558012-20160902213442

"I think the biggest hurtle here is the fact that what hasn't been changed on an article isn't being blanked out so the user's attention is only focused on what changed."

Without the two lines before and after it could be harder to find where on a page a change occurred. This wouldn't be as big of a problem if you had a bunch of paragraphs (which are one line) but in the other instances where there are changes on short lines (take code for example) removing the unchanged lines makes the diff page less useful.