He was also tipped for the top NATO job up until the Biden snub. I imagine that was more painful than missing the PM job (he'd have inherited a bag of wet shit).
Another one of the “safe pair of hands “ on the way out. The Tories are going to be out of power for a while, but it still matters who is left running the party. If there are fewer Wallaces then there’s more chance it’ll be one of the absolute headbangers.