I think one major reason people confess, that I don’t think has been mentioned, is that people fear the judicial committee already have evidence against them, and that if they don’t confess then the lack of confession will be used as proof that they lack repentance.
As I understand it, judicial committees are not up front about what they know. Their opening gambit will be to invite the accused person to confess to anything and everything at the beginning of the proceeding. And anything they don’t mention at the very start, but can be proved later, will be used against them in the decision to disfellowship.
So whether to confess and demonstrate repentance, or deny and hope they don’t have evidence, can present a tricky dilemma.
It's a set up where you can jump one way or the other, only to find out immediately you’ve jumped in the wrong direction.