Because no one scores, and the few scores that take place often look like accidents. If they get rid of the goalies, they might have an OK game.
An American did improve soccer back in the 1890s. He removed the goalies, allowed players to touch the ball with their hands, made the surface a hard surface, and made the nets smaller. It was renamed basketball. Of course basketball has the opposite problem, most of the time...too much scoring rather than too little.