Glad to help the lack in your knowledge. Vatican II came about after two world wars. It also came about after a period where the Pope was really considered God on earth. Church music was often nationalistic, triumphalistic and not really in keeping with the carpenter from Nazareth and his teaching. Much of it was also Monastic and performance based, as was the Mass (a choreography of obedience.)
Obviously, some Catholics got left behind and demanded to get back to the halcyon days where everything was simple (apart from the world massacaring eachother.)
That belief, that the old days were somehow better, still persists with some ageing dinosaurs. Fortunately, most others believe in new wine, new wine skins and the need to be born again.