#1. Former WWE Champion Brock Lesnar
It has been more than a year since former WWE Champion Brock Lesnar was seen in a WWE ring. It appears that there could be a reason for this.
The Beast Incarnate was rumored to be making his return to face Bobby Lashley at SummerSlam. Instead, Goldberg will be the WWE Champion's challenger. Interestingly, Paul Heyman was part of an interview with DAZN back in June where he revealed that Brock Lesnar hasn't returned to WWE because he doesn't want to:
“If Brock Lesnar were to return, if is a hypothetical. Brock Lesnar does what Brock Lesnar wants to do. How you can be cognizant of the fact that Brock Lesnar does not want to challenge Roman Reigns for the Universal championship, or at least not yet, is because he hasn’t done it. Because if Brock Lesnar wanted to it, it would have happened already. And it hasn’t happened already because he doesn’t want to. Now, there may be reasons why he doesn’t want to, and that’s for Brock Lesnar to reveal if Brock Lesnar ever decides to reveal it. Man doesn’t tweet. He doesn’t post pictures on Instagram. He’s not a public persona. He’s a very private beast. He does enjoy being on his tractor and on his combine, and the man loves the farm. If Brock Lesnar ever decides to appear in public, it’ll be when Brock Lesnar wants to appear in public because Brock Lesnar does what Brock Lesnar wants to do.”
Recently there were rumors linking Lesnar to a move over to AEW, but it was later revealed that there was no truth behind these claims.
Update: Lesnar proved speculators wrong and returned at SummerSlam 2021. While nothing is confirmed, it seems he's going to enter into a rivalry with Roman Reigns.