Sometimes it's completely arbitrary. You know how every user has an associated uid? Sometimes we just fire up a script that randomly generates an integer between 10,000 and whatever the current largest UID is, filter out administrative usergroups, and randomly ban that user.
OP had it correct though, when s/he said "I just don't understand". You don't. And your own ignorance, while completely understandable, is not global.
These threads aren't necessary, nor are they advised. I wouldn't plea to have my dirty laundry aired in public, and I can't fathom why anyone else would (except perhaps for friendok but he is a friend, ok?)
the takeaway from this, is "people are getting banned because they've pushed too many buttons they should never have pushed"