Well, forums aren’t a democracy. Ever. And such an election would be a popularity contest quite fast, and moderation doesn’t need popularity. That’s why admin(s) choose moderators and moderators choose those lite-moderators, aka. TL4s.
But if there is a community out there that wants to use a polling system, nothing stops them. The tools are there and if there is a need to get something else, it is just a matter of coding a plugin or component 