#2 Minimising the impact of previous losses
The Undertaker went 21-0 before ever being pinned at WrestleMania and while WWE did eventually do the unthinkable, they waited until they had good reason to do so. Of course, the losses did rub fans the wrong way in the beginning, but its hard to argue that there wasn't sound reasoning on WWE's part behind them.
Take Brock Lesnar for example, who despite being booed for months after ending "The Streak", quickly became the most popular Superstar in the entire company. Furthermore, Lesnar's win over Taker made Seth Rollins look absolutely amazing when he finally took the title off of Lesnar at WrestleMania 32 and went on his six-month tear as champion.
Does WWE really want to minimise the impact of that moment at WrestleMania 32 by allowing another Superstar to join "The Streak" beater club? Doing so would definitely diminish the lore that Brock Lesnar has been building up over the past couple years and really diminish Seth Rollin's cash in as well.
Then there's what it does to Roman Reigns's legacy. While The Undertaker's loss to Roman Reigns did enrage fans a little, it also elevated him to the status of the top guy. Of course, some of that "status" has to do with him rejoining with The Shield, but the win against Taker in Orlando is still a major part of the momentum he has right now.