Why did direct democracy work in athens but not in the united states

Direct democracy was practiced in ancient greek city-states as a form of direct representstion. it meant that each male citizen had a right to speak it’s mind publicly and had equal political rights. the citizens direcly participated in political institutions and had direct control over decision making process. the main reason why is this not possible in the us is because of the size of the coutry. city-states were relatively small compared to the population of the us. some remainings of direct democracy we can see today in the swiss local government organization.