A simpler explanation for the hypocrisy of celebrities who moralize about climate change is that it is a way of flaunting their special status.
Hypocrisy is the ultimate power move. It is a way of demonstrating that one plays by a different set of rules from the ones adhered to by common people. Hypocrisy demonstrates how unaccountable one is to conventional morality.
Such displays work because, unlike wealth, status is inherently subjective. The more of it you are perceived to have, the more of it you actually have.
To be sure, the Duke, the Duchess, and Thunberg didn’t consciously decide to flaunt their status. But neither did Harry and Meghan pledge to never fly private again nor did Thunberg cancel her trip.
And it is a mistake to imagine that human behavior is mostly conscious. Much of human behavior is unconscious and driven by an innate urge for power, of which status is one (highly-social) form.