Why does hentai anime usually suck?

Take a look at some hentai manga or doujinshi.  Regardless of the content, you'll see some amazing art work a lot of the time.
Watch a hentai video.  Terrible, repeditive animations.
WTF?

I just watched the first episode of Urotsuki Doji (the original)!  This rocks awesomely much and is better than 90% of all anime produced today.  I'd say it even improves on the manga in some aspects.