It doesn’t help that government recommendations have been based on either terrible research or straight up from lobbying groups for so many decades.
The old food pyramid was insane. Nuts, beans, and red meat all being lumped in the protein category, while all fats and sweets were considered the same. Sugar was just considered a carbohydrate, whether it came from fruits or from soda (high fructose corn syrup). The categories were displayed and expressed as hard lines and there was no nuance at all. Not to mention bread, cereal, rice, pasta all being the largest category… and an entire category for just milk-based items.
For many people the government recommendation is just taken at face value, often just because that is what they’re taught in school.