The reason why Parisians are so rude in this context, as I've heard from several French natives, is that time is money. Most interactions with tourists in Paris

The reason why Parisians are so rude in this context, as I've heard from several French natives, is that time is money. Most interactions with tourists in Paris are transactional. If a shopkeeper or restaurant server can spend two minutes with one customer in not-perfect French, or 30 seconds in not-perfect English, and there is no recreational value for the Parisian to the slower choice, then the Parisian will renegotiate the discussion's language to the faster choice. You could call that helpful if you're optimizing for fastest transaction. For tourists who might have spent years in school learning the French language, and many recent weeks on Duolingo refreshing before the trip, and who are optimizing for a richer local experience, it's thoughtless and rude. Both viewpoints are rational.