They cannot afford to play too many cards as an answer to them as they will lose consistency, nor can they often rely on card quality, draw or tutors to find the required answers
Gimli, Mournful Avenger Is MTG's Latest Powerful Aggro Commander Gimli, Mournful Avenger's first ability gives him indestructible when two or more creatures die under the player's control this turn
Im also not looking at artifacts or lands unless they have white in their identity, even though you could play them with a mono-white commander, too
You will always be naming Assassins, which will keep most of your creatures on the battlefield
Eternal formats like Legacy and Vintage also encourage lower land counts due to just how low the mana curves of those decks can get
No one can respond, and every creature on the field dies