#2 The Undertaker wasn't satisfied with his match against John Cena on a personal level

Following the debacle against Roman Reigns, The Undertaker really did put his best foot forward. He lost a lot of weight, trained properly, and seemed much healthier as compared to his previous outing at WrestleMania 33. However, The Deadman would only get a three-minute match with Cena and he expressed his displeasure about the same.
"Professionally it was fine, personally it left me a little empty. I was able to train for the first time in a few years in a way that I wanted to train, pain-free in my hips. I was prepared to do a 20-30 minute match."
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The Undertaker even went on to suggest that had he got the perfect match with John Cena in terms of storytelling and obviously the in-ring elements, he could've possibly walked away. But that wasn't to be eventually given how short the match was and The Deadman concluded that nothing much could be done about it.