IMHO, the main reason why the bar is set so low in the US is that if there is a mandatory federal requirement for graduation, there will certainley be a percent of people that wont make pass it and those who won't graduate will probably in a minority due to financial and enviornmental problems.

Once people see how a disproportionate number of minorities of not graduating, they will scream discrimination and then heads will start to roll... So instead of trying to make the system better, politicians just set the bar lower and lower trying to make it seem as if the nation's children are getting smarter