Actually, believe it or not, grinds exist in MMOs because players due enjoy them (timesinks). A really awful feature could not exist if players weren't willing to partake in it, regardless of loot reward.
This is very true in games that has high mat requirements for crafting, which requires hours a day of nothing but mat harvesting. People do it because it's fun for them, with a reward that makes them keep coming back to harvest more.
Grinds originally existed to keep players occupied between expansions (mind you in a day before XBox and the ADHD/ADD it has caused in gaming - small maps; less buttons to push; everything streamlined for the 1hr attention span player). Today grinds are there also as timesinks for people "wanting something to do".
BTW, standing there taunting bosses is a mechanic in EQ, EQ2 and even WoW. WoW is a tad different because of the weapon dps factor (where in EQ/EQ2 multiple taunts damage and hold aggro - a more elegant aggro management way - and you're constantly taunting), but tanks even in WoW often have nothing more to do but to mark targets in raids/dispel/sometimes innervate.
So probably the real issue is some tanks are bored of just standing there. But that's the role of the MT, to draw all the hate onto them so others in the party won't get clobbered, and so casters and other melee can kill the boss/mobs. The perk? MT gets all the loving and buffed out of the kazoo to play that role.