Ban isn't intended to make people behave to begin with, so they didn't lie. People are supposed to behave from the moment the read and agreed to the terms of uses, and ban is meant to eliminate the account they created as punishment for breaking their promise.
Ideally, ban is meant to remove said players from the community, but as you know that's impossible to enforce since they value their own comfort over the rules everyone else abides and would just make new accounts to find their ways back, which isn't preventable.