Still not as crazy as a Democratic president having not died in over 50 years (LBJ, 1973).
That's really a combination of two things: Republican dominance of the White House from 1969-1993 and both JFK and LBJ dying young. I suppose you can add a third thing and that's the sole Democrat to hold the White House during those years of Republican dominance happens to be the longest-lived President in history.
After Truman and LBJ died (within a month of each other), there were no living former Presidents until Nixon resigned. There were also 21 years between LBJ's death and the next President to die (Nixon).
Prior to Walter Mondale in 2021, this applied to Democratic VPs as well.
Humphrey died in 1978, so that would be just over 43 years. That's still a considerable amount of time though. As far as Democratic VPs go (including two that became President), five died within just a bit more than 12 years (November 1965-January 1978).