#4 To make way for younger WWE talent
There's a reason why The Undertaker was the WWE locker room leader for so many years, when he was an active competitor. It stems from the fact that he's always been a team player and thinks about what is best for WWE. He realizes that he will be a draw as long as he is alive. However, it may be time to make way for the new generation.
When he appeared on the Sam Roberts Wrestling Podcast, Big Cass spoke about how The Undertaker gives advice to young talent like him, in the locker room. The Undertaker realizes that he's had a great run, and it's time that younger talent carries his legacy. We deem it quite likely that he'll take a backseat very soon.
Charlotte Flair to return and wrestle a CURRENT CHAMPION?
After all, there are so many talented individuals who do not have a singles match at WrestleMania. They will either be booked in multi-man affairs, or thrown into a Battle Royal.
If The Undertaker hung up his boots, a spot would open up for youngsters.