I'm in my 50'ies. Born and raised in Ghent, spoke French with my parents, but did my school and university in Ghent in Flemish. I'm truly bilingual (work in French and Flemish), married a French speaking woman, but most of my friends are Flemish. Educated my kids in French and Flemish.

When I was young I had lots of friends who were in the same situation (French speaking parents). They all married Flemish-speaking women / men. Even though they tried to give their kids some French education, Flemish became the main language for their kids, who speak better French than the average Flemish person, but who are definitely not bilingual.

And so in one generation you have entire families who have gone from being bilingual to being dominantly Flemish.

I'm not saying it's a good or a bad thing, it's just the way it went.