#3 Taking a valuable spot from a younger Superstar

A WrestleMania match can make or kill a Superstar. A great showing at WrestleMania can increase a WWE Superstar's stock exponentially. Seth Rollins put on a great match with The Miz and Finn Balor in last year's show which helped him build great momentum which led to a Royal Rumble win earlier this year.
It would be cruel on a talented Superstar's career if his spot on the show is taken by a 53-year-old veteran who makes 1-2 appearances a year, while younger Superstars work week in, week out to earn their right to feature in WrestleMania.
With so many talented Superstars on RAW and SmackDown, as well as many waiting in the wings at NXT, a match featuring The Undertaker compete against another legend or one with no build or storyline, does not make sense.
The likes of Elias, Drew McIntyre, or Mustafa Ali deserve a match at WrestleMania more than The Undertaker, at the moment.