>30 years is not long enough for everyone involved to be dead and no longer influential... and that doesn't even touch on whether the reason it happened is structural.

Context matters. With the end of the cold war, the oligarchy doesn't get to use a threat to gather support. And a certain level of diversification of those economies have made the very powerful less power.

My second point is that half of South America had left wing government and there was no Coups. Things would have been very different for Lula or Correa in the 70's.