I really think, from observing the many posts critical of priests, bishops, and questioning the validity of the sacraments they receive, that most of these come from young, unmarried, and often newly-converted Catholics. Some of the posters in these forums actually do promote an atmosphere of mistrust in our clergy to do the right thing. And people are always being advised to find another parish, report things to the Bishop, write to Rome, etc., when in reality all we have is the word of the poster reporting something that may or may not be as they perceive. This does nothing to give some people confidence in their leaders.
The Sacrament of Marriage, however is usually entered into with the confidence that everything is a-ok, validity usually isn’t even an issue when one gets married, and the priest or deacon does not confect the Sacrament–they are witnesses for the Church. There is no way usually that a couple in love is going to think about the possibility they are entering into an invalid marriage. They may not be clued-in to some of the signs, such as a drug or alcohol addiction that MAY affect consent, or ignore signs of potential unfaithfulness, thinking things will change once they get married, or signs of mental illness that may affect consent. They may have even been warned by someone or by clergy that there may be a problem, but deny it or choose to ignore it. So often validity doesn’t even enter the picture until the marriage falls apart and a declaration of nullity is sought.
That’s why I think there is such a discrepancy.