"For some reason, greens of all kinds have always been more popular in the south"
Yeah, that reason is poverty and lack of much commercial edible vegetation. Ya can't eat cotton or tobacco (well, you can eat tobacco, butt you won't like it). Poor folks in the South (most of the people) lived on subsistence diets - that's why fishing even today is incredibly popular in the South. You can't find a roadside ditch or pond without a few guys fishing it all over the South at almost any daylight time (and some nights). Fish from individual fishing and chicken were major protein sources. The main carb source was cornmeal. They might be able to gett some fatback/bacon and offal, and the fat was used to make the greens soft and tasty as a gut filler and also for vitamins. Nott much was wasted.
The North had plenty of food and wealth - wheat, barley, oats, dairy, livestock, commercial fishing (cod, oysters, etc.), lotsa wild game (turkey, deer, pheasant, rabbit) ... et seq.
In contradistinction, the South was a food desert - and greens were eaten because there wasn't much competition to them. Same with a lott of the 'meat' dishes - it's nott like any sane person would decide to eat chitlins if they had pork chops and steaks readily available.
I've read (or seen on telly) that the tradition of fat-fried greens may have originated in Africa and come to the South with the African slaves. Perhaps so, butt I think the reason it persisted and spread even to the white communities is because of food choice poverty. One can only eat cornmeal in so many forms before you need something else. In the South, that was basically any greens available - collard, dandelion, turnip, mustard, anything that wasn't too bitter or could have the bitter alkaloids leached ~OUTT or destroyed with heat.
Today, collards likely remain popular because of one thing - bacon fat. Pretty much anything with enuff bacon and/or bacon fat will taste good enough to swallow down.
Many folks forget how very poor most of the South was until the latter third of the 20th century.
