An average player usually uses there grenades pretty quickly, often times at the first gunfight.
That player who wins should be rewarded with the enemies grenades. This allows this player to have an equal advantage with the next player who just <mark>respawed with grenades</mark>.
Not only is this a <mark>disadvantage</mark> for you, it makes the game slightly less entertaining. (Maybe just slightly, but dont we want this game to be the best it can be?)
Halo Multiplayer is all about being able to anaylyze a varity of given situations and reacting to them according to the weapons you have at your disposal. By not allowing us to pickup up grenades, your taking out variety from Halos multiplayer. And if you want that variety back, you have to actually pick an armor mod. Armor mods shouldnt detract from multiplayer without the use of it.
Its something that could possibly be patched in the future. Grenades at their current state are pretty weak compared to Reach’s, so balance would not be compromised.
I believe inability to pick up grenades is an issure because it detracts from the varity of the game, it subtracts deserved reward for slaying, and there isnt a reason for it not to be an ability!!