I know there were many rites before the Reformation. However, in order to ensure that Protestant innovations deep not creep into the Mass which was happening in Europe: e.g. Archbishop Von Wied was introducing liturgical changes in Cologne written for him by the reformer, Martin Bucer.
Any rites less than 200yo were suppressed so that no novelty elements could be introduced. Policing a host of different rites and uses to keep them free of doctrinal error would have been difficult. Other rites and uses such as those of Milan, Toledo, the Dominicans and Carthusians continued.
St Pius V's action, far from being "an historical anomaly" was designed to save Christendom from fragmentation. Incidentally, if, as you assert, it was "an historical anomaly" then how much more of "an historical anomaly" was the Mass of  Blessed Paul VI when there was no threat to the Mass from Protestants or anywhere else?