Why can I say,'Why do you like her so much?' but not, 'Why do you like her very much?'
My answer is: 'Why' is evaluative and forces you to make (or consider) a comparison. Very cannot be used in comparative constructs.
A friend of mine raised the point: That 'very' seems to work in the negative form. For example: "Why don't you like her very much?"
Any ideas?
Cheers,
Scott