A point which few seem willing to concede is that catechesis was far more formal and extensive prior to Vatican 2 than it was after; not because of Vatican 2, but because “progressives” objected to both a doctrinally focused and a rote memorization method of teaching (i.e. the Baltimore Catechism) and wanted to go to a “Gospel based” (i.e. “evangelical” format; and the bishops massively failing to step in to the matter - as well as priests - failed to see that children were receiving a very watered down catechetical upbringing.
Coupled with that was the inroads secularism made into people’s lives, along with the start of the breakdown of the extended family due to a far greater mobility of people post WW2. And the matters above affected not only those in Catholic schools, but the greater majority of children who did not attend those schools, but had a once a week “CCD” training.
the result was that those born a bit before Vatican 2 had weak religious training; and matters got weaker from there on out. Fast forward 50 years and we now have two generations who lknow little about their faith raising the third generation. In 1957 we hit the peak of Mass attendance at aobut 67%, and it gradually has gone down to somewhere around 22 to 23%; and in the age bracket of 18 to 29, it is about 18% (per CARA).
People have a natural tendency, it appears, to try to find fault, as in moral guilt; I leave that to God to deal with, and a confessor should they choose to find one. Much of what a tribunal seeks to determine is not “fault” as it is facts; again, I am not going to outline the multitude of issues which may result in a decree of nullity as they are well outlined in the books I recommend.
Another point that people miss is that it may be the party starting the process for a decree of nullity who is the person who had the impediment or defective consent consent, or it may be the other party, or even possibly both.
Contrary to popular opinion among those who do not understand the actions of a tribunal, the Church is very serious bout the sacrament of marriage; and they take the position that marriage is a whole lot more than simply showing up and saying some words. It goes both to freedom to marry (as in, impediments which would prevent it) and intent- of which there are multiple issues which could be grounds.