#2. The only way to entice Goldberg to return
Make no mistake about it. Just because Saudi Arabian officials wave a lot of money to bring back legends, it doesn't mean that it's an easy task. You can be assured that convicing Goldberg to come back required a lot of negotiation and a lot of time.
The ball was obviously in Goldberg's court, because he had the leverage while WWE likely insisted on getting him. Knowing that they needed him for the show more than he needed them, he knew that he had the leverage of choosing his opponents.
Check out which wrestler EC3 finds cute RIGHT HERE
If you think about it, it's like hitting two birds with one stone for Goldberg. Not only does he get to face a legend that he's never faced before, but he just has to go for a few minutes at a relatively decent pace to earn that big paycheque. Perhaps no other program interested him much apart from Undertaker and Roman Reigns.