You can find a lot of high-calorie cuisines: German, English. Some of this is a matter of supply, no doubt: when hens are laying and there's a cow that's milking, a medium-sized farm family is likely to be very well-supplied with eggs and dairy. But there's another angle, and that's where the calories went. Look at the furniture in use in the typical 18th colonial American house. Big, overstuffed chairs are rare. Most people made their living by farming, and were on their feet most of the day.

Many Southern dishes trace their roots to the black slave population. Rice, grits, manioc, sorghum, etc are all foods that were commonly grown in West and Central Africa during the period of the Transatlantic Slave trade. These societies which were providing most of the people for the slave trade grew these foods and their meals were typically comprised of one starchy staple foods which are high in calories (like those I mentioned) and maybe a bit of meat and vegetable. These food practices were eventually carried over from Africa to the Caribbean and Antebellum South where they became part of the culinary culture.

As for butter, sugar, and cream I cannot say... But the history of starchy foods I got covered.