Mobius and pet octopus
Member
Because Taskmaster is just too useful to keep in your hand for a play that consumes an entire turn and can be easily thwarted by a lot of things. Use Taskmaster on Acolyte/Armorsmith to get more use out of them and to enable them to trade with better minions, use it on enemies to combo with Execute or BGH (in extreme situations), use it to just kill something at 1 health, etc. I don't want to hold it in my hand for the sole purpose of enraging Gromm. Besides, Leeroy + Faceless is the same 12 burst damage for 1 less Mana. You will be holding Faceless in your hand anyway, waiting for a big threat to be played and stay on the board, if no such thing is played, use it on Leeroy to burst your opponent down. Since the 12 damage is spread on two creatures, BGH won't do the trick for them and it's easier for me to get around taunts. Leeroy is also much more useful to me outside of this burst damage than Gromm. Use him as a neutral Fireball to clear big threats or just for 6 damage to the face, play him with Whirlwind to clear the Whelps and buff your Berserker, etc.
Leeroy best case scenario; Leeroy + Inner Rage + Faceless = 3 cards, 9 Mana, 8 damage + 8 damage
Grommash best case scenario; Gromm + Taskmaster + Inner Rage + Inner Rage = 4 cards, 10 Mana, 16 damage
I don't run Inner Rage, so that becomes;
Leeroy + Faceless = 2 cards, 9 Mana, 6 damage + 6 damage
Gromm + Taskmaster = 2 cards, 10 Mana, 12 damage
Worst case scenario:
Leeroy = 1 card, 4 Mana, 6 damage.
Gromm = 1 card, 9 Mana, 4 damage.
I just don't see a huge upside to Gromm, since he is actually more vulnerable in some ways. You can silence Gromm, you can't silence Leeroy + Faceless. Gromm is putting all eggs in one basket, Leeroy is spreading it out over two minions with the opponent only being able to kill one with the Whelps. Gromm is killed by Execute and Big Game Hunter, Leeroy isn't. Gromm is stopped by a single Taunt minion, Leeroy + Faceless can kill a Taunt and then deal 6 to the face.
And then there's the combos. Let's say you have a Berserker on the field and your opponent plays a Taunt minion. Leeroy + Whirlwind + Execute = kill their taunt, buff your Berserker with +5 attack, clear the Whelps, 13 burst damage to the opponent.
Gromm is pretty much restricted to being a finisher. Leeroy is just so much more versatile.
Same as with Taskmaster, I think Whirlwind is just too useful/versatile to keep specifically to buff Gromm. It can net you some extra use out of you Acolyte/Armorsmith, serves as a setup for Execute, can get you insane armor with Armorsmith and multiple minions on the field, can buff your Berserker to insane status and can just be used to clear damaged or pesky 1-health minions without needing to drive your own minions into them (Buzzard/Blood Imp/Young Priestess/Murlocs/Loot Hoarder/Leper Gnome/etc.). Sometimes, double Whirlwind can even be worth it.
I just don't want to hold it in my hand for just using it to enrage Gromm.
I think it is also important to note that warrior has many ways to enrage grom, plus if you use the buff on a minion and hit face, you're getting the 2 damage anyway. It is kinda like saving cold blood for leeroy... there is no point (almost). You get the 4 damage either way and if you use it earlier there is a chance you get to hit with it twice. Same with tinkmaster. The only reason you'd want to save tinkmaster is if it is your last tool to activate grommash and/or you are concerned about something like alexstrasza or lord jaraxxus.