Here's why:
* Sadness is a subjective experience: The intensity of sadness varies from person to person and situation to situation. You can't objectively measure sadness and say one person is "sadder" than another.
* We use other words to describe different levels of sadness: Instead of using comparative forms, we use different words to describe varying levels of sadness, such as:
* More sorrowful, more melancholy, more dejected, more heartbroken, more despondent for a higher level of sadness.
* Slightly sad, a bit down, mildly unhappy for a lower level of sadness.
Example:
Instead of saying "He was sadder than her," you might say:
* "He was more sorrowful than her."
* "He was more heartbroken than her."
In conclusion, while "sad" doesn't have direct comparative or superlative forms, we can use other words and phrases to express varying degrees of sadness.