They backed themselves into a corner. If Cody wins, it means Cena's heel turn was pointless and he really has no business being in the main event anymore. It's also his best chance to break the record.
If Cena wins, he's going to be a part-time champion and barely defend the title. Then that leaves the WHC which Jey will have to drop sooner than later, or they'll have to create a new championship which they already did. I'm not sure what the right choice is, but I know that they have to get something out of Cena turning heel.
Also, unlike Hogan, Cena isn't actively taking away people's spots or stealing TV time. He's been putting guys over nonstop for years. The last time he main evented WrestleMania was the last time CM Punk competed at WrestleMania. And it's his retirement tour. So they have to do it big. Most fans can understand why he's getting the title match this year, especially after the heel turn.