We say all of these things out loud. And in plural. But even in a bad year, we haven't done all of these things. In Reform synagogues we recite an alphabetical acrostic of sin, first in Hebrew, and then in English. It has to do with the psychology of the human spirit.
Some traditions treat confession differently.
It is private, and individual. They thought that, for all of us, if we stand up, if we recite the whole list together, if we say the words out loud, but with no one looking at anyone else, if we are not singled out, but supported by the voices of a full community while looking in our own souls, that in that moment it might actually be easier to be completely honest with ourselves than if we were the only one talking. It is a wise strategy, if an ironic one, that during the one service of the year with the biggest attendance, surrounded by the largest number of other people, we might be able to find ourselves. To hide no more. And begin to heal.