I think it’s because the thing is either too obvious (if you’re native) or too specialized (if you’re a linguist). E.g. Chinese seem to also have a strict adj. order, but we only got to study it by pure chance.

I would also guess that many languages that usually don’t have a strict order will have parts that do, e.g. in Spanish it seems you may shuffle some words but not everything

The image above transcribed:

1. Opinion – limiter adjectives (e.g. a real hero, a perfect idiot) and adjectives of subjective measure (e.g. beautiful, interesting) or value (e.g. good, bad, costly)

2. Size – adjectives denoting physical size (e.g. tiny, big, extensive)

3. Shape or physical quality – adjectives describing more detailed physical attributes than overall size (e.g. round, sharp, swollen, thin)

4. Age – adjectives denoting age (e.g. young, old, new, ancient, six-year-old)

5. Colour – adjectives denoting colour or pattern (e.g. white, black, pale, spotted)

6. Origin – denominational adjectives denoting source (e.g. Japanese, volcanic, extraterrestrial)

7. Material – denominational adjectives denoting what something is made of (e.g. woollen, metallic, wooden)

8. Qualifier/purpose – final limiter, which sometimes forms part of the (compound) noun (e.g., rocking chair, hunting cabin, passenger car, book cover)

Big bad wolf.