#2 WWE is still hesitant to pull the trigger
Unfortunately, this might be the most likely reason why Kofi Kingston didn't win. Can you count the number of times that WWE didn't capitalize on a superstar that was red hot. You probably lost count.
Just going back to more recent years like 2016, we saw Dean Ambrose become the hottest superstar in the company. Fans wanted him to main event WrestleMania and win the WWE title, but WWE decided to push Roman Reigns anyway.
In 2018, something similar happened, but to Braun Strowman. Superstars not being capitalized during the hottest season of the year is not uncommon, and it's very likely that WWE is just continuing the trend with Kofi Kingston.
After all, they probably want a big name like Daniel Bryan walking into WrestleMania as WWE Champion and aren't sure how Kofi Kingston will draw with the WWE title.