I think the people who want the world to be vegetarian for non-health related reasons (e.g animal rights advocates, environmentalists) push the largely discredited "saturated fat is bad, carbs are good" dogma because saturated fat is mainly present in meats and not in vegetables with some rare exceptions such as avocados and tropical plant oils. Also, carbohydrates are not present in meats, but plentiful in vegetables.

The scientific consensus is that saturated fat is a risk factor for cardiovascular disease, having been endorsed by many medical, scientific, heart-health, governmental and intergovernmental, and professional authorities, such as the World Health Organization,[1] the Food and Nutrition Board of the National Academy of Medicine,[2] the American Dietetic Association,[3] the Dietitians of Canada,[3] the British Dietetic Association,[4] American Heart Association,[5] the British Heart Foundation,[6] the Heart and Stroke Foundation of Canada,[7] the World Heart Federation,[8] the British...

https://en.m.wikipedia.org/wiki/Saturated_fat_and_cardiovasc...

Actually a lot of these xx Is bad for you are dubious or just well marketed fads eg lo salt as my specialised NHS dietician (for chronic kidney failure) commented they don't tell you what C$%^ the put in to replace salt