A really good question indeed. The corpus-based approach is good at showing you what you see - or even what you never think you will see, but never tells you why that is so. You will need to use other methodolody and knowledge - maybe psychology and siciology in this case - to find out answers to such questions.
This is what Louw (2000: 52) says -
The fact that negative prosodies are more frequent than positive ones ought not to surprise us greatly. In the same way that unrequited love forms most of the subject matter for the greatest love poetry in English and not requited love (with the superb exception of John Donne's The Good Morrow), we ought not to be surprised to find that contented human beings utter much less than discontented ones. Besides, requited love is a fairly busy and time consuming state and one which is as inimical to the act of writing. However, if fracture and discord are the basis of unhappy contexts of situation, then the over-provision of intimacy, comfort, food, drink and possessions are likely to form the basis of contented situations. John Sinclair long ago indicated to the author (personal communication) that the author might find the positive prosodies clustering around forms such as warm.
The concordance for warmth and bears this out and creates scope for the investigation of positive prosodies with objectivity rather than schmaltz. However, it should be noted that this concordance for warmth and (Appendix 3) does not single out a semantic prosody, because its authorial function hardly rises above the banal and it fails too on the related criterion of pragmatism. It is a good example, however, of the strong provision of connotation.
Can you think out a more reasonable explanation?