It occurs to me we are probably talking apples and oranges here. My fault no doubt. You are talking about ground fighting arts and mention BJJ, and I am talking about grappling arts such as the art I studied, Hapkido. We learn ground fighting techniques at higher levels, but more with the intent of getting back on our feet as quickly as possible. We don't prefer to be on the ground, but prefer to defend while on our feet, using grappling moves, and we can work against more than one opponent as can many other MA, but it isn't preferred by us any more than most martial arts.
A couple of things occur to me though, that might be worthy of discussion in this thread. First, I really know little about BJJ. However, do they really intend to do most of their fighting on the ground, or is that just their way of doing damage before getting back up as quickly as possible to take on any other possible attackers? Is Karate or TKD ineffective because they don't have ground fighting, or more effective because they employ blocks, strikes and kicks that make it more dangerous to try to take a them to the ground?