During slavery and even after, whites who owned plantations did not want to provide blacks with proper foods and nutrition. They sought for foodstuff that was cheap and abundant to feed the many slaves. In Jamaica, for instance, the slave owners sought foods from many sources, including from the South Seas and India. When Captain Bligh (from Mutiny on the Bounty) came back from the South Seas with BREADFRUIT, which was very filling, the plantation owners were happy because they could feed the workers without giving them better, if more costly foods which they saved for themselves. What made the Caribbean, specifically Jamaica different is the fact that there were so many tropical fruits and wild boars (pigs) that the slaves could sneak and cook underground, which is where the concept of jerk meat and barbecuing originated (from Jamaica).
In the US, the slave owners gave the slaves WATERMELON, pig snouts, intestines (chit'lins), hog maw and all the parts of the animal that they deemed to be waste, undesirable. As you may already know, watermelon is very filling. Therefore, it is no wonder that they fed it to the slaves and later, to the sharecroppers. In essence, black people learned to make lemonade out of lemons. The watermelon, which is a delicious fruit, is just another sometimes unpleasant reminder of what blacks had to work with in order to survive in the US. I say, what God has blessed, let no man curse!