What factors might have made the roman empire more stable than the roman republic

Praetorian guards

If the empire has 2 emperors the Praetorian Guards kills the one they don't like. If there are 3 or more then the Praetorian Guards just have to kill until there's a single emperor standing. And if that emperor betrays the Praetorian Guards then they can just kill him and sell the crown to the highest bidder.

Despite so many civil wars, Rome always survived. Because the greatest and most trained fighters in history always held command. They were also the richest fighters in history.

If a bordering nation becomes too powerful and actually becomes a threat to the empire all they have to do is go there and kill them.

They were corrupt. They were unstable. But they kept the country going. Until Constantine decided to get rid of them. And the Roman Empire fell a century after. The Roman Empire died with the Praetorians.

Romans would always attribute the stability and success of their empire due to the virtue and strength of their men as well as the will of the gods.