The difference isn't simply age. The difference is the discrimination against one of two equally valid measures of medical fitness and capacity to operate an aircraft within a certain category and class triggered by age of the pilot. At age 80, the opinion of your personal physician must be superseded by the opinion of a government agency if you are to obtain insurance, the opinion of which data to this point proves to be of no better predictive value.
Additionally, the government's opinion, though no more predictive, may require certain expensive and time consuming tests which place an increased burden on the the older pilot.
Insurance can only discriminate against you if there is in fact greater risk. It could be argued that a Basic Med pilot in fact presents no greater risk than a Cl3 after age 75 or 80 than before.