You are confusing two very different things. It used to be that each person individually had to confess their sins out loud in front of everyone. .
True, but there were only three sins which had to be confessed out loud in front of the congregation.
If memory serves me right, apostasy, murder and theft. Other sins like adultery did not have to be confessed publicly.
But even then, it was not always done and absolution was given to the entire congregation.
Private confessions at that time where absolutely prohibited by the Pope.
It wasn't for centuries until private confession came about, and it originally was for spiritual guidance.
In the past hundred years or more, confession has digressed into mostly the a penitent rattling off a list of sins and the priest giving a penance of prayers which was pretty much the same for every person, then absolution.
Even my last pastor, he gave no spiritual direction, just two Our Fathers and absolution. Everyone I know, got the same penance.
As it is, the majority of Catholics don't go to Confession, but they receive Holy Communion anyway.
Making general absolution at the penitential right at Mass, helps to assure the individuals are not in a state of sin when they receive Holy Communion, which is a sin in of itself, but few know it.
Jim