Source: The Wrestling Observer
The current plan in WWE is to keep The Undertaker off of TV until WrestleMania 31. That means that he will not appear on RAW or SmackDown to help build to his match with Bray Wyatt at WrestleMania.
The idea is to create mystery as WWE fans don’t know where ‘Taker is, what he looks like, what condition he’s in or if he’ll show up at all. WWE believes that this will lead to a surprise when Undertaker actually shows up at WrestleMania 31 to fight Bray Wyatt.