They can't have been that popular.
Why?
CDM was a marketing decision to make the most eaten chocolate brand. It had nothing to do with Wispa's success or otherwise.
What I am saying is Cadbury didn't create CDM with Picnic, CDM with Fuse, CDM with Starbar, CDM with Boost, CDM with Time Out... if Wispa was that popular they wouldn't have incorporated it into that range.