The sacrament of confession, although not restricted by any means to the Roman Catholic Church, has found its development in a unique way within that denomination. It is addressed at some length in the Catechism of the Catholic Church. Here are just a handful of paragraphs -
1424 It is called the sacrament of confession, since the disclosure or confession of sins to a priest is an essential element of this sacrament. In a profound sense it is also a "confession" - acknowledgment and praise - of the holiness of God and of his mercy toward sinful man.
It is called the sacrament of forgiveness, since by the priest's sacramental absolution God grants the penitent "pardon and peace."
It is called the sacrament of Reconciliation, because it imparts to the sinner the love of God who reconciles: "Be reconciled to God." He who lives by God's merciful love is ready to respond to the Lord's call: "Go; first be reconciled to your brother."
1484 "Individual, integral confession and absolution remain the only ordinary way for the faithful to reconcile themselves with God and the Church, unless physical or moral impossibility excuses from this kind of confession." There are profound reasons for this. Christ is at work in each of the sacraments. He personally addresses every sinner: "My son, your sins are forgiven." He is the physician tending each one of the sick who need him to cure them. He raises them up and reintegrates them into fraternal communion. Personal confession is thus the form most expressive of reconciliation with God and with the Church.
1456 Confession to a priest is an essential part of the sacrament of Penance: "All mortal sins of which penitents after a diligent self-examination are conscious must be recounted by them in confession, even if they are most secret and have been committed against the last two precepts of the Decalogue; for these sins sometimes wound the soul more grievously and are more dangerous than those which are committed openly."
When Christ's faithful strive to confess all the sins that they can remember, they undoubtedly place all of them before the divine mercy for pardon. But those who fail to do so and knowingly withhold some, place nothing before the divine goodness for remission through the mediation of the priest, "for if the sick person is too ashamed to show his wound to the doctor, the medicine cannot heal what it does not know."
The question of this thread is - Where are the lines of people at Catholic churches prior to mass waiting for confession?
When I was young, each Catholic church of the ten large parishes in my otherwise small city was staffed by at least four priests who regularly heard confessions. Each church had multiple confessionals for this purpose and they were kept busy.
Today, the parishes are, if anything, numerically larger following the closure and consolidation of many parishes. Of the surviving parishes some do not even have a full-time priest and the rest which do, count themselves fortunate to have one individual priest. Whereas in my childhood there were typically three or more masses on Sunday, today a Catholic church typically must make do with one Sunday mass a perhaps a Saturday evening mass, if they are fortunate.
Now, the Catholic Church is clear that one cannot take communion unless one has met the requirements, which includes undergoing the sacrament of confession. If a church (at least the ones in my neck of the woods) has 1,000 faithful parishioners, all of whom attend weekly mass and who take communion, the time required to hear their confessions would not be insignificant. Even at the breakneck speed of five minutes per person, it would require 5,000 minutes for the priest to complete the sacrament for his flock. For those who are curious, that is well in excess of 80 hours, which is more than three days with no breaks for eating, sleeping, or other physical necessities.
Now, some may say that my example is too large. Okay, so if there are only 100 communicants that still would require 500 minutes, which is well in excess of 8 hours - with no coffee breaks, bathroom breaks, or meal breaks.
That leaves several possible reasons, which I have handily provided in my attached poll.
I am absolutely certain that I will be accused of not providing a reason that some can find acceptable, but I don't claim to be the best pollmaker at CF, or, for that matter, even a good one. So, if you don't like my choices, then don't respond to it.