I think there were positives and negatives to V2, but I don’t think V2 is why people quit practicing their Catholicism. Most likely they would have quit even if V2 hadn’t happened. People want to use birth control, get divorced and remarried, have sex and live together before marriage, maybe even have abortions, etc and they don’t want to hear a church telling them it’s not OK, nor do they want to be told they need to go to church every Sunday or else.
In past eras (up through about the 1950s) there was a big social stigma attached to most of the above things, with the possible exception of birth control, but the Pill hadn’t been invented yet so birth control wasn’t as prevalent or as effective as it became when women could just take the Pill. The Pill also caused a huge increase in previously forbidden sexual behavior, like sex before marriage, because the fear/ risk of an unwanted pregnancy was greatly reduced.
Add in the clergy sexual abuse scandals that have plagued the Church since the late 1980s and the fact that so many priests and religious during the 70s and 80s didn’t act in ways that would command respect and in many cases just quit their religious vows or even quit the Church entirely, and people have more excuses to leave… “well who’s that priest to be telling me what to do when the priests are all committing sex scandals of their own, and quitting the church so they can marry ex-nuns” etc.
It’s pretty easy for people to walk out on a church that handing them difficult teachings and going through scandals when they don’t have much idea why they were even going to church in the first place, didn’t have a personal connection to Jesus or the Eucharist or didn’t think experiencing Jesus through the Catholic faith was important. It’s not like keeping a traditional Latin Mass would have fixed this problem by making everybody more reverent or making them see how the Eucharist was important etc.