(IMO, the Francophone solution, to annex the predominantly French-speaking areas of Halle-Vilvoorde to Brussels and then split the district, is quite reasonable, but the Flemish oppose it because it creates geographic continuity between Wallonia and Brussels, which the French-speakers could use to kill innocent Flemish babies, or something like that.)
It's psychologically important to have Brussels entirely surrounded by Flemish territory. Every year, Flemish Nationalists cycle round the city to prove this point (seriously).
