#2 Why he should retain: Royal Rumble might not be the best place for this title change to happen
Royal Rumble is one of the biggest WWE pay-per-views but it is not the biggest. Wrestlemania, the Grandest Stage Of Them All, is the biggest WWE PPV that is just a few months away to happen.
Even if Strowman wins the Universal Title at the Royal Rumble then it may not benefit him a lot. Especially considering the fact that the company is in a shortage of big names.
WrestleMania, on the other hand, is the biggest event of the WWE and whoever wins at this event gets a lot more exposure. Lesnar is one of the biggest superstars in the WWE and if Strowman defeats him at Mania, it would make his career.
However, the fans may not like see Lesnar defeating Strowman again but there's still an option. Instead of losing the match clean, Strowman could defeat Lesnar via disqualification.