User blog comment:Elphrihaim/Clarivoyance...?/@comment-1990160-20130807201752

It would seem that you weren't here for S1. In competitive S1 play, 'all supports carried CV/Flash. If you didn't have CV as a support, your team basically lost map control. CV already had a decent skill cap, in that a bad player can't use CV for anything.

With S2, Riot decided to bury it with higher cooldowns and reduced sight duration. This, combined with the meta shifting to speed junglers in S2, made CV fairly worthless. Junglers are general play have shifted towards increased mobility, which makes CV less useful, as its high cooldown doesn't allow for optimal usage against fast junglers.

Hmmhmm... other points... supports are usually the player that takes Exhaust, which is guaranteed to have utility in teamfights. Also Sightstone has made increased warding easier.