Here's why:
* Indivisible: You can't have "one humor" or "two humors." Humor is a concept, not something you can count.
* Usage: We use "humor" in a general sense, not with specific numbers. For example, we say "He has a good sense of humor," not "He has three humors."
* Plural form: "Humors" is an archaic term used in medicine, not referring to humor as we understand it today.
However, there are some cases where you might use "humor" in a countable sense:
* Types of humor: You could say "There are many different types of humor," referring to categories like slapstick, satire, or dark humor.
* Jokes: You could say "He told a few humors" to refer to individual jokes.
But even in these cases, it's more common to use "types" or "jokes" instead of "humors."