Paying a name chef to associate with the airline meals is a way to announce the airline cares about its food. And if consumers believe the name chef cares about their reputation at all, they won’t put their name on the food unless it meets certain standards. It’s also not very expensive for an airline to rent the chef’s name relative to the total cost of the meals provided.
A celebrity chef doesn’t guarantee a good meal, in fact if a chef is putting their names on an airline meal you should downgrade your estimation of the chef. It means they’re more interested in the revenue stream from branding than maintaining quality for the simple reason that they cannot possibly replicate the restaurant quality of their means in the air, heated in an airplane galley, and plated by US airline flight attendants.
