There are “kingmaker” senators in both parties that cross the aisle occasionally, that this rule benefits (and also generally their specific constituents, sinc

There are “kingmaker” senators in both parties that cross the aisle occasionally, that this rule benefits (and also generally their specific constituents, since their outsize influence gets them more than they might otherwise get in negotiations.) Given that these kingmakers are what causes things to go over 50-50 they want to preserve their power.