Why was Paul de Man prevented from returning to the Free University of Brussels after the war?

Paul de Man was prevented from returning to the Free University of Brussels (ULB) after World War II because the institution had implemented a ban on individuals who had collaborated with the German occupation forces.1

During the war, de Man had worked for German-controlled media companies and the newspaper Le Soir, where he contributed an anti-Semitic essay and promoted pro-German sentiments. Following the war, these organizations were investigated and found to be treasonous. Although de Man was interrogated regarding his employment and writings, he was neither prosecuted nor exonerated at that time.1