The association of Undertaker and Smackdown was a deliberate strategy on WWE's part. If you take a look at any Smackdown commercial presentation from 2002 to 2010, you'll notice that Undertaker was nearly always the prominent feature. He was the visual embodiment of Smackdown. This is perfectly evidenced by Smackdown's introduction video. Undertaker would close the montage as the main man. He was the reliable marketing point that WWE knew would bring viewers in.
