I've seen this kind of thing too many times to count. First it was in high school, then the workplace.

1. Person notices there is no explicit rule for a thing, or maybe there's a loophole somewhere
2. Does the thing
3. Annoys someone
4. Now there's a rule for the thing

Some people just want to push the envelope. Other times, people can have a poor grasp of social norms, or they simply don't respect others. But on the other side of the coin, people get annoyed for good and bad reasons; sometimes, no reason at all.

Bottom line: it's a mess, so we get rules. But nobody wants to spend time writing these things and enforcing them, so there's usually a reason/person/event why they're there.