Shouldn't the campaign be encouraging cyclists make themselves more visible?

There are already many campaigns encouraging cyclists to wear light-coloured or reflective clothing, and these have been around for decades. The advice is also in the Highway Code.

The Stop SMIDSY campaign is more concerned with the response of the authorities when crashes and near-misses involving vulnerable roads users actually happen. It aims to address what our society can do to protect our most vulnerable road users, rather than putting the onus on cyclists and pedestrians to protect themselves.