Warriors rejected because of no Obsidian shard

[Ashimar]

"Rogean: Taunt puts you at the top of the aggro list. If you are already at the top, it does nothing. However it does fail a lot, and it doesn't have a visible fail message, so just keep trying until you have aggro, then stop using it until you lose aggro."

So why do warriors use Obsidian Shards for aggro when they can just taunt?
Is it because if taunt does fail, the proc from the weapon serves as a "taunt"?

or do people scowl at warriors to use Obsidian shards because of the 30 DMG
proc helps to lower mob HP strictly?

Whats the deal here people?