Why didn't the border states join the confederacy? (Short Animated Documentary)

From History Matters

During the American Civil War the border states of Delaware, Maryland, Kentucky and Missouri had a tough choice to make. They were all states that permitted slavery and none of them had voted for the newly inaugurated President Lincoln. So why didn't they leave and choose to join the Confederate States of America instead? Why did those states opt to remain in the Union? To find out watch this short and simple animated history documentary made by someone who can't draw or animate but don't wor...