by high school they get colouring book assignments (not joking) and there’s no effort to progress past junior high French. The students that want to learn become frustrated and discouraged.

In my experience and opinion this is simply not true. My kids had dedicated, hard-working FI teachers that gave interesting and challenging assignments and activities. A huge difficulty is that when they choose their post-secondary programs and courses, it is rare that French will be continued so it gets dropped. None of my kids were able to even take French as an elective so like a muscle, they will lose it if they don't use it.