^may be it was the greed for the power? or envy is a real evil thing. For example in Bukhari, Umar is recorded to have said they he was jealous that Imam Ali got the flag from the Allah and his Prophet at the khyber.
so if umar was really so jealous that he hated ali he wudnt have mentioned that in ali's fadail and the whole tenor of the report is a positive one for ali