And the real kicker is that really good people are sometimes not good at saying the right thing, or may be too depressed to be able to say much, while some others are great at lying and acting repentant, so the percentage is probably far worse than that.
That's even supposing they are entitled to judge anyone's else repentance in the first place. The bible just says you shouldn't associate with anyone called a Christian who engages in immoral behavior. It doesn't say it's a formal arrangement, just something you would do if you know yourself that someone is engaging in a long term practice of sin. Nowhere does it say a committee is formed, or three people get to judge you for making a mistake. As Jesus said "let him who is without sin cast the first stone". There is no determining of repentance, repentance is shown by stopping the behavior.
Nothing in the bible indicates that people are disposable, that they can be cut off from family and friends at the whim of a few elders. They don't even give people a chance to repent, but act as judge, jury and executioner. The person then has to live with being shunned for a year or more before they will even be talked too, all the while going to meetings and being humiliated on a weekly basis. Finally they may be allowed in, if they kiss enough butt to "prove" their repentance.
Many can't stomach that level of humiliation and give up, and who could blame them? The worst sin in the bible is stumbling one of your own brothers, so who is really the sinner in this equation?