the Roman obsession is just simply Vince's ego. he's usually been able to get the crowd behind the wrestlers he hand picks, but it's not working this time and it's driving him insane. it has been a complete failure for 5 years now hurting ratings and other wrestlers potential money along the way.
Vince can't accept the fact that the guy he personally chose has been completely rejected by the overwhelming majority of the fans so he's continuing it simply out of spite. He's not gonna stop the obsession until someone in corporate gets other shareholders together and force his hand.
Roman Reigns still being in the spotlight in 2018 is 100% a "fukk you" to the fans from Vince