I once said to a priest friend of mine, "There used to be only a few hundred annulments in the whole United States before Vatican II. In the last fifty years there have been thousands of marriage annulments every year. Has something gone wrong with marriage tribunals or are there really that many Catholics living in objectively invalid marriages?" He didn't hesitate for a second: "Both."
We need to define some terms. Catholics throw around the word "annulment" a lot but what they mean is a declaration of nullity. The word annulment implies that a marriage was there but it has been erased by the authority of the Church. A declaration of nullity means that a couple may have gone through the motions but no true marriage ever existed between them. The marriage didn't end; it was never there. Nothing that happens after vows are exchanged can retroactively nullify a marriage. If a declaration of nullity is made by the diocesan or Roman marriage tribunal, it means the conditions for it existed before the wedding ceremony. Some of the conditions are:
1. A so called shotgun wedding. If vows are not freely exchanged, there is no marriage.
2. Marriage to someone closely related by blood. Siblings and first cousin weddings are right out.
3. Getting married outside of the Church without a dispensation.
4. One or both parties is already married, even if it's only civilly.
5. One or both has already taken a vow of chastity.
6. The man is impotent and didn't reveal this to his bride.
7. Too young.
8. One party is unbaptized.
9. One or both parties is incapable of giving true consent.
That last one was traditionally understood to mean either retardation or insanity, but now it's used as the pastoral lever to nullify a great many marriages: "We were young and didn't reeeeally understand what we were getting into," or "If my husband's an alcoholic maybe he didn't really give his full consent back then." Basically, if anything at all unexpected happens after the vows are exchanged, that can be used in the tribunal proceedings as evidence of nullity. This is a big problem. If the tribunal grants a false positive, then two innocent people are turned into material adulterers. For that reason, the tribunal must always err on the side of declining to grant a declaration of nullity. The annulment grant rate in the United States is about 97%. American Catholics divorce at pretty much the same rate as the general population. A declaration of nullity is a permission slip for the priest to witness a new marriage, but I imagine that Catholics who know about how tribunals work must live in a terrible state of uncertainty. We shouldn't find it surprising that most people now think of this process as getting a Catholic divorce.
The blame for the explosion in annulments does not rest solely upon the shoulders of diocesan tribunals though. Many lay Catholics really don't understand what sacramental marriage means. They go in to it believing that divorce is a real possibility given the right circumstances. They might agree beforehand to live a "child free" marriage through contraception. Given the general breakdown in catechesis at every level, it's not outside the realm of possibility that there really are that many invalid marriages out there. People who strongly dissent from Church teaching generally don't go to confession much. People who are grossly ignorant of the faith might know or care about their ignorance. Most Catholics will get married though so it behooves Holy Mother Church to think about this problem seriously.
The solution is to tighten the requirements both for annulments and for marriage. Marrying outside the Church? Your marriage is invalid. Marrying a non-Catholic without a dispensation? Your marriage is invalid. You intend to never have children through using contraception? Your marriage is invalid. Do not rush them through preparation simply because they're shacking up and you want to bless a sinful arrangement. Being a hardass may not make you popular, but it may save your neighbor's soul.