According to Wrestling Observer Radio, Lesnar has wanted to work with Balor dating back to last year's Rumble. However, in January of 2018, it was reported that Vince McMahon didn't see Balor as a main eventer, let alone a candidate for the Universal Championship.
Lesnar went on to have a triple threat match with Braun Strowman and Kane and was set for a redux with Strowman this year. But injuries, timing, and circumstances dictated that WWE call an audible for the Rumble and Lesnar's endorsement of Balor may have granted the Irishman the huge opportunity.
Per The Observer, McMahon
Apparently, Balor vs. Lesnar has been the plan for a while now but continued to promote the Rumble with Lesnar and Strowman headlining. This apparently was inspired by the motive to move ticket sales as WWE is hoping to fill out Chase Field on January 27. WWE used a similar motive for Evolution but advertising Alexa Bliss vs. Trish Stratus for weeks, despite knowing that injury would keep Bliss from working the match.0comments
Ticket sales aside, Balor vs. Lesnar should inject some much-needed excitement into WWE's fanbase. No one was thrilled to see Lesnar installed as emergency Champion after Roman Reigns was forced to take his indefinite leave. Given that WWE used Reigns to "rid" themselves of Lesnar at SummerSlam, giving the belt right back to The Beast was as necessary as it was unpopular.
Even though Lesnar vs. Strowman would have been fine, the Universal Championship has a freshness about it now that Balor is involved. For what's felt like ages, the big red belt has belonged to Lesnar with the understanding it would one day be Reigns. But with Reigns out, it seemed like STrowman had the obvious claim to the throne. But now that Balor is involved, it may signal that WWE is ready to diversify that scene and open up their top title to more Superstars, not just a rotation of two or three big names.