The GOP E promised him more - if he runs again anywhere for office they will make sure he wins. That’s the way it works anymore like we see from this election.
The GOP would certainly not be above that, for sure. It would certainly explain why somebody, who honestly, does not have a chance at becoming the nominee, would stick around.
Typically, people who run for the nomination, who have no chance, are doing it solely to raise their profile so they can win elsewhere.