Why is "any" not classified as an article?

Answering the question, Use of articles with adjectives, got me thinking. Why is the word "any" not classified as an article? We learn in grade school that the three English articles are "a", "an", and "the". Later on we learn that articles are part of a larger class called determiners.

Numerous dictionaries, including this one, declare any to be a pronoun and determiner. But look at this sequence:

a --> an --> any

(Should I drop the mic now? Nah, I'll continue in case any of you feel stubborn. 😉)

Whether you agree or not, think about the following:

1. The word a is one of the indefinite articles for singular nouns, used before a word beginning with a consonant sound. A cat is sleeping.


2. The word an is one of the indefinite articles for singular nouns, used before a word beginning with a vowel sound. An owl just hooted.


3. The word any is the indefinite article for plural nouns, regardless of what the next word is. Are there any red shirts? It may sometimes substitute for a and an to force the specific context of "one among many". [e.g., "plural-like"] Any book will do.


4. The word the is the definite article for nouns, both singular and plural, regardless of what the next word is. It supports multiple contexts, but always offers definiteness:
   
   
   
   
   • The Mona Lisa smiled at me. [uniqueness]
   
   
   
   • The black kitten smiled at me! [one among many (definite form)]
   
   
   • The three kittens with white paws were so cute! [some among many]
   
   
   • We found homes for all the kittens. [all]
   
   


5. Neither a nor an can be used with a plural noun. If any is not an indefinite article, a plural form does not exist.

I discern two differences with the accepted indefinite articles. The first is that any can also be a pronoun. Any of them will do. So what? The word a can also be a noun, the first letter of the Latin alphabet. Do we really need the second a of aardvark?

The second difference is that any can force the specific context mentioned in item #3. The (other) articles force a context as well, indefiniteness or definiteness. This is illustrated in the following conversation between two kids:

An ant bit me!
Which one?
I don't know, but it wasn't the one on your arm.
Damn! Any ants are too many. I don't want any ant to bite me.
I know, right? Let's go see if we can find a bandage.

In other words, a, an, any, and the all force contexts. That's sort of their point. So why is any the one left out?