Ron Burgundy
I look good...
I think it goes back to there is just no need. If an alt is being used for humor, then why not just post it under one name. The only reason I can see using an alt is because you are being such a jerk that you don't want to "sully" your main name, you are trying to get around a ban, or you are wanting to fake fight between two accounts.
Personally I don't see any of those as valid reasons for having multiple ID's. I can't speak for HD, but that is my take on it. If you have to hide behind an alt to say something, it probably doesn't need to be said
They do it to annoy people... and not risk their main account being banned.