It's supposedly the reason the French are historically known as the best sauciers. It was to mask rancid meat.
There's also an economical factor. Poorer people were forced to eat the scraps and bad cuts of meats. They used lots of spices or long cooking methods. Some of our most beloved foods originated with the poor. Look at soul food: gravies (smothering), ham hocks & greens, pigs feet, gizzards.