Ezreal and tear of the goddess

I like playing support more than any other role, however, lately though the role has become really unresponsive to my teams ability to take objectives and make fight altering impacts in the game. Mainly though its the downturn in quality adcs that has been the biggest downer on me wanting to queue up for the roles so guess them queue times are going to get longer for me. Anyways the question I want to pose is this. Why do people take tear on Ezreal? Sure it becomes a muramana late game which for most ezreal builds gives him an additional 70 attack damage, but wouldn't it make more sense to build an essence reaver which gives sighly less attack damage but gives you 20% critical strike and additional cooldown up to 20% just building 30% critical strike from other sources? To me it seams like a sweet deal to get 50% critical plus mana back for those criticals while maxing out my cooldown with an iceborn gauntlet all the while no making your support scream in frustration at your pathetic weak mid game because "I'm charging my tear". Is it really that great an item to take the risk of throwing your mid game on the chance you'll get to late game and have slightly more damage? Thoughts? Try to leave a little more than a few words if you care to respond.