Why aren't peanuts, pecans and almonds real nuts?

Nuts have a specific botanical definition, so here

The 10 Healthiest Nuts To Eat, According to Nutritionists

Nuts! What They Really Are and How the FDA Classifies Them as Allergens

Pecans- Everything You Need To Know – Ayoub's Dried Fruits & Nuts

Can I Eat Almonds if I Have Peanut Allergies?

We're nuts about nuts- and you should be, too - Mammoth Bar

Nuts - CooksInfo

In a nutshell: Different nut types, explained, Grains, Legumes & Nuts

Choosing the Best Nuts For Nutrition, Snacking, and Cooking

Which nut is more nutritious, peanuts or almonds? - Quora