Those big hubs airport do handle local/regional/national flight too, even though it would bring more stress for some VFR pilot to land there, they can.
The thing is, there are known misunderstanding in english as well, you can listen to american ATC recording of foreign not understanding anything, because of an accent, or “conversation” outside of basic phraseology, etc…
Because there are more than one way to get a PART.FCL.055, some requires you to “SPEAK” english, while some simply requires you to pass a practice exam in simulated flight condition (basic phraseology…). All of them being certified exams. For instance, the DGAC exam for english is more of the later.
As for pilots, it’s their job, doesn’t mean they “like” to speak english, especially, imagine an Air France Paris - Nice flight, with a full crew of french speaker, french dude on the receiving end, and they have to switch to english just because some people think it causes misunderstanding.
It adds added stress more than anything, in a job we don’t need that. Also those flight are so short, they’re mostly typing things into their onboard computer all the time and it’s already time to land. Very busy.
A french dude speaking english with a french accent, to a french dude speaking english with a french accent, it’s definitly giving higher risk of misunderstanding
Unless you want all ATC to be english native speaker with perfect speech, and requires everyone to validate a level 5 or 6 fluency in english, even new pilot students, all over the world.
Thank you for providing the actual part of AIP that justify the use of french on the territory by the way.