Your question directs me to think that most French women have gaps in their teeth. I have never read about it anywhere, so I went on to hunt for it on the research databases. Sadly, there is no report that French women have more gaping than other ethnicities.
I found an interesting study which explored the cause and effect of diastema in Indian population.(1) Sadly, they were not able to pin-point any specific condition as a cause.
There is incidence of diastema in cleft lip and palate patients and also the patients going under an orthodontic treatment called ‘rapid maxillary expansion’, but there is no relation to French women anywhere. If you have a reference, please put it in the comment section and I will edit this answer.