I'm reading though your responses trying to figure out what mysterious force is present in this hypothetical proportional representation country that prevents a

I'm reading though your responses trying to figure out what mysterious force is present in this hypothetical proportional representation country that prevents a majority subset of parties B - Z from forming a coalition. Can't figure it out. On the assumption that Party A just simply has the majority still? This objection lakes cogency, so maybe you could make this general objection more concrete by citing a country that finds itself in your abstract scenario?