#4 The Fiend's streak doesn't have to end
The Fiend's winning streak has to end sooner or later and while one would imagine it happening at WrestleMania, it doesn't necessarily have to. Beyond that, if The Fiend were to take on a WWE veteran and not an up and coming superstar, it could allow the company to make it a statement victory for the Universal Champion.
At least that way, WWE doesn't need to have The Fiend's streak end, they can use it to make the character a legendary figure and no one has to deal with the resentment of someone ending the streak. Just remember how badly Brock Lesnar was booed after ending The Undertaker's streak and you could see where that would be a problem.
With that being said, having The Fiend take on The Undertaker at WrestleMania 36 would do two very important things. The first is that it will allow for The Fiend and The Deadman to play off of their parlor gimmick in order to distract from Taker's limited move set. The second thing it will do is allow for Wyatt to have the passing of the torch moment he should have had years ago and not suffer a loss that could derail him.
Now, this doesn't mean that The Fiend's streak shouldn't end eventually, but not at WrestleMania. Furthermore, not when they have a chance to officially establish him as the biggest thing in the company. Keep in mind that opportunities like this don't always present themselves, which is why it needs to be capitalized on.