User blog comment:Zambu/Useless passives/@comment-4794115-20130501183133

Taric's old passive was kind of useless for a support. If you're taking the time to melee minions to get your mana back, not only are you pushing your lane but you're gonna get wailed on by enemy adc.

His new passive, along with the changes to make him more effective for building tanky, gives him a lot of free damage and encourages you to build mana as opposed to mana regen.