His reign was long, prosperous, peaceful. As the years passed, people forgot how bloody and chaotic previous transitions had been, as there was no serious attempt to bring about a change in who wore the crown.
So much so that when he did finally die, there was a period of mourning where a quick, dignified rise of one of his children to the throne was possible.
Of course, the longer the delay, the more likely a reversion to the old ways would be, as not everyone agreed on the best choice.
But all the children dying with him complicated everything...