<<I think it's mostly about what we're used to.>>Partially yes and because of this there's no market, we don't allow one, let's say.
Every now and then I can enjoy a translated movie, usually an animation movie. I do prefer the Flemish version more than the Dutch version. A nice example is the movie Surf's Up. Watch that movie in Flemish, it's hilarious because of the different dialects, especially the Westflemish Chicken Joe
And the reason animation movies are translated in Belgium is because of the kids.