No one has responded to this, so I'll give it a try. Just my opinion: It's not in the rules because including it hasn't been necessary. People generally avoid voting for their own photos. A vote for one's own work can easily be written off as biased, and it may well be biased. It comes off as something like bragging even if what you made really is the best one of the bunch. So we graciously choose among our competitors and leave judgments about our work to them.Although I don't see it in the rules, I assume I am not allowed to vote for myself
None of this applies to candidates for public office.