Widespread failure to die would cement culture in place, and the power structure. It necessarily would dramatically slow down cultural evolution, which strongly depends on funerals. Logan's Run had the right idea, just the wrong number. We old geezers must make way for civilization to effectively adapt to a changing environment.

Even if our lifespans become merely 200 years, imagine if the generation of the US Civil War era were still in power. Great age plus health equals social petrification.