Short answer: Because it's easier to manufacture a plausible sounding excuse than to rethink a large portion of your life.

Long answer: Read the article.

If I learned 1 thing from the COVID pandemic, it's that science doesn't matter when it's at odds with established big money continuing to make big money.

Per the WHO, processed meat is in the same category of carcinogen as cigarette smoking. That's the science. In my locale of Toronto, they sell dollar hotdogs weekly at the ballpark of the professional men's baseball team. They dump tons of money into advertising and fetishizing binge meat-eating. They try to increase the stadium's consumption that day well past 40,000 'dogs'. Last I checked, colon cancer is the second-leading cause of cancer death in men and second in women. These dollar hotdogs certainly keep colonoscopists in business.

More money talk. 2/3rds of animal biomass on this planet is 'livestock', which is given three-quarters of the antibiotics we produce. A healthy vegan is very unlikely to need diabetes, cholesterol-lowering, or heart disease meds. Most people on North American-ish omnivore diets will be on multiple prescription meds of these classes for decades of their life. They will need colonoscopies every year or two, starting around age 50. They will need hospitalization and maybe surgery after their first angina attack, heart attack, or stroke. They're essentially a different kind of livestock.

It's amazing how much taxpayer money goes into preserving this extremely-dettached-from-reality status quo that benefits pharmaceutical companies, the medical industry, and Big Meat. It's not serving the people who eat North American-ish omnivore diets, the healthcare system, the tortured non-human animals, or the low-paid humans that are probably stuck in those barbaric industries for lack of access to better work

Money

because of a century of brainwashing propaganda put out by the meat industry, funded by taxpayers

Bias confirmation. People have to justify their carnist consumption, and an easy way to do that is to claim the other side is equally unethical.

A lot of the processing and multitude of ingredients is also done, specifically because people want the flavor, texture and look of meat, cheese etc.. There's tons of vegan options for protein that have 1 ingredient and 0-2 processing steps.