Why did France become all Catholic?

France is about 86-88% Catholic. Many famous French nationals were or are Catholic such as Jacques Cousteau, Jacqueline Auriol, Brigitte Bardot, getting more spiritual, Probably more modern saints came from France than other European countries, this would include Saint Vincent De Paul- who founded various charities ( still extant) and with Ste Louise de Marillac- the Sisters of Charity, well-known female siants such as Ste. Catherine Laboure ( of the Sisters of Charity) Bernadette of Lourdes, and Theresa of Lisieux have been French. I"d say they were the biggest Catholic power- not without some schisms and jolts, outside of Fair Italy itself. During the so-called Babylonian captivity ( not in the mid-east)- For about 40 years Babylon France was the main seat of the church, which inspired the Folk song about everybody doing the dance on the Bridge of Avignon, which was in the same region of France. So it went. Many Saints from France.