Some of the reason for the upsurge can be that you have given permission (knowingly or unknowingly) for your details to be shared by an organisation you have a relationship with, to their partners or third parties. They sell these lists of contacts as they are a valuable commodity, think here of Banks, Google, Facebook, Yahoo, Microsoft and many others who gather your personal information and in their T & C’s and Privacy conditions have your agreement to share your information with others.
Renewing your DNC cancels any currently in place authority but the sale of a new listing voids the DNC registration and allows the sharing.
See the following topic on more about businesses selling/on-selling personal information
