#4 To protect AJ Styles even in defeat
Aleister Black is a very heavily protected babyface in the roster who wins a lot more matches than he loses, and it was necessary for him to pick up a big win against AJ Styles to advance to his WrestleMania program. But then again, AJ Styles has a very prominent place in the roster too, and WWE couldn't afford to have his legs cut out from under him before his WrestleMania program.
And so, with The Undertaker showing up at Elimination Chamber, WWE protected AJ Styles even though he lost the match. It was a great way to utilize the whole No DQ situation as well because of which Karl Anderson and Luke Gallows got involved in all the action.
One wonders what the next step for Aleister Black is and, in fact, if he will be involved in the AJ Styles vs. Undertaker feud. I wouldn't be too upset personally if he was to be involved in the United States Championship picture feuding against his wife and Andrade.