Why don't dictionaries employ both positive and negative claims when defining a word?

In Do dictionaries make negative claims?, Mitch commented,

"I think what you're getting at is not any sort of negative in a definition but rather an exclusionary part of the definition. That is, using a more general definition and excluding portions of the general set. eg, "mitigate means to make things better than they were but not necessarily good". Is that what you're wondering if it is actually used in a dictionary?"

to which you reply

Yes, that's probably a better phrasing of what I wanted to ask.

The problem is that such qualifications are potentially endless.

The phrase, "mitigate means to make things better than they were but not necessarily good"

could be 'improved' to become

"mitigate means to make things better than they were but not necessarily perfect or even good"

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The drawback of all English dictionaries is that you need to understand English in order to read them. Therefore the dictionary makers have to assume a basic level of understanding.

A reader is expected to know already that "better" does not mean "perfect" or "good". In this case what the extra information has done is to include a partial definition of another word (better) in the definition of the word "mitigate".

If we have to explain all the words in a definition within the definition itself, we have a hopeless situation. It may not be infinite but the size of such a dictionary would be beyond all reason.