I think it's the nature of the game. American football draws its structure from American military doctrine. You have a commander on the field. He constructs a plan which every member of the team understands and attempts to carry out. However once the ball is launched the team, knowing the goal of the play adapts and works the plan according to their on-the-spot judgment and skills. Coach Tom Landry moved the actual play calling higher up the chain of command and freed up the quarterback to massage the plan based on on-field knowledge and found that the strategy was devastatingly effective.
Baseball is a series of one on one duels with the pitcher backed up by fielders.
Soccer is a world sport that is modeled on a never-ending conflict model. We have American field sports like lacrosse, hockey and basketball that contain elements of soccer, but in deference to our collective ADD, we have more frequent goals and opportunities to reset built in to those than they do in "futbol". Even Rugby which is a bit like American Football in some respects, lacks the decisive quarterback type position and the setpiece battles of the American version.
Football is rather like a short violent serial version of chess. The quarterback sets his pieces, lays his strategy and then cuts his team loose to see how far they can move the ball. It's unique. It's the difference between American and French politics. With traditional American politics, there's a discreet pitched struggle and then it ends at the voting booth and boom, you have a government. With the parliamentary system as it is in most countries in the soccer-loving world, the voters may decide who gets elected, but it's the politicians who actually "form a government". They may fail at it and the country may be in turmoil for months while the politicians kick the political futbol back and forth. In the US the voters elect a government and if they don't like them, they elect another one two years later (or six years with the senate/ 4 with the administration). American football has that same character. We can pitch out the quarterback and go with a backup after every play if we don't like what he's doing. In virtually any other sport pulling out the team captain wouldn't make all that big a difference.
So, just like there's only one United States of America, there's only one American Football. Just one man's opinion. Tom King ;-)