Very much this, and especially over this period. More universal diagnostics, more emphasis on secondary causes and contributors, etc.
And it works the other way, too. Fewer people should die per capita based on faster EMS response times, better medicine, more urban living, etc.
The big one for me is age. I never really heard of people retiring to Arizona until the late 90s. It was always Florida before then. The over 50 crowd is 36% now vs 23% in 1970.