So, why is a doctrine and procedure created based on only what Paul said?
In a legal setting a person that is disorderly or breaks a law can be trespassed from private or even public property for a year or longer because he is encroaching on others. In a church setting or JW community a member who breaks the rules and doesn’t want to stop disrupts the practicing of religion by others in the group. If he doesn’t stop, he is put out. Fundamentally, this makes sense.