The current WWE Universal champion Roman Reigns who is also a five times WWE World champion recently revealed the actual reason behind the return of the former eight times WWE world champion Brock Lesnar.
At the “Biggest Party of the Summer” WWE SummerSlam of this year, WWE Universal champion Roman Reigns defend his Championship against the former 16 time WWE World champion John Cena on the main event of the pay per view. Roman Reigns successfully defended his Championship as he defeated John Cena and pinned him with a Spear.

Roman Reigns Reveales Why Brock Lesnar Returned
After Reigns defeated John Cena, the former eight times WWE world champion Brock Lesnar made a surprise return and dudh face to face with Reigns. He did not say anything but his intentions were quite clear. He wanted a shot at the Universal Championship. After the show went off air, Lesnar beat down John Cena.
Whatever reason that Roman Reigns or other wrestling personnel say, it is quite clear that the WWE brought Brock Lesnar back just to give a good competition to their new Rival promotion the AEW.
With CM Punk making his AEW debut, it would not be easy for WWE to compete with the promotion unless they bring some big names. This must have been the reason why big name live Brock Lesnar and Becky Lynch are in SmackDown. So that they could compete with AEW Rampage.

champion Roman Reigns who is also a five times WWE world champion recently spoke on The Bump where he revealed the actual reason behind the return of the former eight times WWE world champion Brock Lesnar. He said;
“I’d be lying if I said it wasn’t a big one, but for me, the next win is always the biggest win. So, yeah. It’s on the next one,” Reigns responded. “Obviously, you already know who stepped up [after – Brock Lesnar], at least, and made it appear that way.”
“I think he wanted to get the best look possible and see what’s going on. I’m the most dominant Universal Champion that’s ever done this thing. I think he sees the Island of Relevancy, just like John Cena did,” Reigns said of Lesnar’s return. “He’s just coming with like a farmer, butcher outlook as opposed to being the Hollywood guy.

“But, yeah. It just goes to show all this work; this foundation of greatness I’ve been laying down continues to show we’re number one. They want to talk about it, but it’s just for them to put themselves in the conversation with me to amplify everything. But there isn’t anyone who can compete with what we’re doing.
“Between me, my cousins [The Usos] and the wise man [Paul Heyman], we come together, and we’re putting together greatness. We’re lifting the bar. We’re lifting the standard. I think Brock Lesnar, like everybody else in this industry, they want to be a part of that.”
H/T to WrestlingInc for the quote