I don't see why this isn't existent.
We don't have this because it's not part of the software. If we wanted this, someone would have to do custom coding.
I personally put things like this at the very bottom of my to-do-list. I think that we have a million better things to do than the improve the communication between moderators and people who like to break chat rules. Lets not forget that this reason for a ban and its duration would only benefit maybe less than 1% of chat users, because that other 99%+ never gets banned.
An easy fix to this problem is
not to break any chat rules. Sure, it might annoy you not to know how long of a ban you got, but why didn't you break the rules in the first place?