Negative questions usually show the speaker’s expectation that the response should be positive.
In the English Grammar Profile, B1 point 12 in the category of NEGATION is defined as:
negative question forms in main clauses and question tags.
This is such a general point that overlaps and clashes against so many other points in the English Grammar Profile. For example:
an uncontracted question for emphasis is C2.
For that reason, we won’t bother developing this post much more. The others are more specific.
EGP examples with corresponding examples:
Don’t you like pizza? (A2 or B1?)
Why don’t we watch a film? (A2)
Why can’t the English see what the Scots and Welsh can?