Lived in Paris for a year and this is 100% the reason, according to Parisian waitstaff I knew. Same for the Brits.
Apparently the reason is the french motto “Liberté, Égalité, Fraternité”
They take that shit seriously. Every job is equally valuable and to be respected. You speak to and treat a waiter or a cleaner the same way you speak to a doctor or a lawyer, they’re all égal humans
A sizeable portion of American and British tourists treat waitstaff like animals, and cleaners as though they don’t exist, then wonder why they’re rude to them