Money has definitely changed the food pyramid over the years. Various lobbies, and all.
But to your points about vegetarianism/veganism, I think the reason most people who try these diets have poor outcomes on them is because they unwittingly end up eating more ultraprocessed foods that are actually worse for them than what they ate on their previous diet. Most packaged "vegan" options are just awful. Ultra-processed TVP is as bad for you as cured meat in the long run.
My wife and I are on a "mostly" plant-based diet, and we do it with fresh fruits and vegetables, not ultraprocessed "imitation" meats and other garbage like that. I eat between maybe 8 and 16 ounces of meat in a normal week, and it's fresh meat from a local farm, not packaged, cured, processed, dyed, antibiotic'd, hormoned meat. It makes a huge difference.
I would venture a guess that the high cholesterol problem came about with ultra-processing of foods in the 1960s and 70s. More chemicals, more industrial food manufacturing, less nutrition in fruits and vegetables due to monoculture and mega-chemical farming, etc.. A lot of the chemicals used in the ultraprocessing of foods are probably toxic and inflammatory, and cholesterol production and plaque buildup is one way your body can defend the epithelial cells in your cardiovascular system from these toxins in your blood. It just so happens that this can also kill you.
Now, here's the ultimate problem. There are too many people. Eating healthy food requires agriculture that is free of pesticides, herbicides, hormones, altered DNA, chemical growth stimulants, and ultraprocessing. The amount of land we have could not possibly produce enough healthy food to feed everyone, and it can barely produce enough garbage food to do it. So, good luck solving that one.