Ranking on mobs in a group at least
(i) is a somewhat social experience (occasionally there is enjoyable rp, even if not it is a way to get to know people and build IC friendships)
(ii) allows others to attack your ranking group thus increasing their (and occasionally also yours) pk fun
(iii) allows newer players to see skills/spells of other classes, ask about gear, etc.

On the other hand if I run alone through some remote area looking at the same shit with yet another lowbie character this has no positive externality whatsoever.

I guess the idea was to give an edge advantage to more experienced players but this could have also been achieved in ways that actually enhances the experience for others.