#4 Fan reaction
WWE has pulled off some pretty amazing feats over the course of the company's history, but to have Brock Lesnar outlast 29 other men in a Royal Rumble match would be a pretty big ask. Not to mention the fact that it would be a widely unpopular decision and could lead to some resentment heading into WrestleMania season. That's something WWE absolutely does not want going into the most important time of the year.
In fact, anything less than a shocking elimination will probably have fans booing and demanding that WWE stop relying on Lesnar so much. That's why the company needs to go with the much more predictable outcome and just have Lesnar leave the match early after being eliminated.
At least that way, the conversation shifts to the Superstar that eliminated Lesnar; the company can keep the WWE title on the Beast Incarnate and no one has to take a needless loss. It will also possibly help gives fans a positive outlook on the pay per view and the road to WrestleMania, which is very important.