How is an email thread with multiple branches any different than the comment tree in this post? What makes it less comfortable and why is it a nightmare compar

How is an email thread with multiple branches any different than the comment tree in this post? What makes it less comfortable and why is it a nightmare compared to how the comments are rendered? The only difference is that you could have to click on each comment to read the body of the message, but the tree structure would be the same as it is now.