"If medicine is so effective at extending our lives on average, why is it so ineffective at extending the upper limit?

meaning:

it refers to how medicine is great at fixing illnesses or injurieslike cancer or heart attacks and getting people to live exceptionally longerafterspecific diseases (like childhood cancer cured and the child dies at 85) or injuries (Civil War had 600,000 deathsmostly of infection or likewise)But not good at extending the length of life as in old age, which is maybe 100 years.Why can't we live to 150 reasonably?