The reason, however, may not be clear as the stats are rather deceiving. This runeword doesn't have any % Enhanced Damage, which means the weapon damage will appear unchanged from the weapon base in the item 'stooltip and the character screen.
Still Grief has huge added flat damage (+340-400 damage). Furthermore this bonus is added to the weapon's dmg when applying any plus %dmg modifier on any other piece of your gear, like 30-60% enhanced dmg from Steelrend, or +350% dmg to demons from Laying of Hands.
Also other stats like 30-40% Increased Attack Speed, Ignore Target's Defense, 20% Deadly Strike are very desireable modifiers in any melee weapon and elevates the runeword's DPS even higher (and all the rest are noteworthy stats).
Grief's added flat bonus will be used when calculating Smite dmg.
Grief only takes a single High Rune ( Lo) to make so overall it likely has the best cost-benefit of all melee runewords.