I don't know why there's no backlash against this.
And by the way - in Belgium, parties have to pander to the French or the Dutch voters; in Switzerland, the different language regions have different voting behaviour; in Germany, east Germany votes significantly differently, as does Bavaria; and so on. Voter blocs are not something exclusive to the US, even if the history of the black population doesn't have a direct parallel in Europe.
Well it's a bit different, as people in Wallonia can only vote for francophone parties and people in Flanders only for Flemish parties. Only Brussels gets both. So in effect, parties don't really have to choose whether to pander to the French-speaking or Dutch-speaking voters.
Which is even worse IMO, because how can you form a functioning federal government from parties that are each elected only by half of the country? Well you can't, as the current situation shows.