@Quincy,
Quincy wrote:There is no such rule to my knowledge. It is only common that people do it. Sometimes you see people use no commas at all: "Four long white cotton shorts" is also acceptable.
Indeed there is no such "rule", and if there is no requirement to indicate that some adjectives in a sequence are coordinate and some are not, then the commas can be dispensed with, but sometimes their use is required to avoid ambiguity and if the sequence of adjectives is a long one, can perhaps aid readability.
Consider the following sentences:
Quincy's first well-written clear intelligent thoughtful essay.
Quincy's first well-written, clear, intelligent, thoughtful essay.
Quincy's first, well-written, clear, intelligent, thoughtful essay.
Which one would you prefer to see in a written message from your teacher?