That's not purely a TdF thing, we call the Vuelta and the Giro by their local names, without resorting to Spanish or Italian for anything else during those weeks. I think a lot of the other stuff is French, simply because that's who named them. Derailleur was coined by a Frenchman, just as fajita or carne asada was coined by a Mexican. Who wants chicken in a flat, corn disc? I'd rather have a taco. It only becomes disingenuine when you invent new terms for things, simply to make them sound more exotic. Like Hagen Dazs.