Quote Originally Posted by CorvinusV View Post
A tank's core function is to tank.
Correct! Tanks do this by making sure they have the most enmity of the rest of the party, the vast majority of which comes from attacking and dealing damage, AKA dpsing. It is not a great leap of logic to think that by jumping into dps stance when you have aggro solid, that the extra damage you'll be dealing will be helpful in also keeping aggro, and unlike with healers, tank and off tank numbers are actually calculated, meaning that them maximizing their dps has legitimate, meaningful gains, rather than being a crutch to help the undergeared dps do their job. Incidentally, 3 of the 6 single target aggro gen moves are a part of the dps rotation for a reason.