Corn smut is a plant disease caused by the pathogenic fungus Ustilago maydis that causes smut on maize and teosinte. The fungus forms galls on all above-ground parts of corn species, and is known in Mexico as the delicacy huitlacoche; which is eaten, usually as a filling, in quesadillas and other tortilla-based foods, and soups.
Quesadillas are often eaten in Mexico.
Nothing in the text suggests they are eaten often or where they are often eaten. It's difficult because the text contains the words Mexico, usually, and quesadillas in the same sentence which perhaps confused it.