Maybe my guess only, but France has its bit of a technological centralization. I mean, a lot of people use internet from operators like "Orange" / "Free", and in contrast to other countries, routers provided by the operators in France do not suck. The routers are OEM, but overall quality you get from them is on-par with Ubiquity/Mikrotik.

This gives operators a benefit of the vertical control for the whole ecosystem - from top to the bottom, including intricate parts of protocols and routing. And France, in contrast to other countries, does not suck here too - operators usually do a good job of meticulously maintaining their assets.

My personal impression is that this is the result of several cultural factors:

1. Ingrained respect of privacy, private property, and a peace of heart as they call it. As a practical result of that, you do not get spammy messages and ads from operators, banks, etc. You may get some, like 3 or 4 discounts/offers in a year. Compare that to other countries where you can easily get 10s/100s messages like that in a single day. In other countries, instead of upgrading the infrastructure, people are busy with spamming each other.

2. The harsh oceanic environment with hurricanes and storms fosters an appreciation for reliability and functionality. It also encourages a certain frugality: every cent matters. As a result, people tend to develop a strong sensitivity to situations where form is prioritized over function, and such approaches are quickly dismissed as impractical. This gives a certain internal freedom of being able to see through things to determine what they are in the long run and not what they appear to be on the surface.

3. French people don't like to overwork outside of working hours. So choosing something like IPv6 over IPv4 seems like a natural forward-looking investment for the future where you can have less maintenance burden and thus you can devote more time to enjoying other things in life.

Having all those things combined, it's not hard to see why France chose IPv6. It's a natural choice there and it's imposed by survival.

P.S. I've spent some time in France, but was born in another country.