This is part of the CAA initiative to cut the excessive regulation of GA and move to evidence based regulation.
Experience with the reduced medical requirements for the NPPL has shown no evidence of increased accident rates.
Private pilots in general are safety concious people and are capable of deciding not to fly when unfit.
Many years of global evidence has demonstrated that medically related accidents are rare in aviation and usually the result of unpredictable sudden incapacitation. The word "unpredictable" here means that no regular medical examination could have predicted the outcome.