So the point is that in the past, it didn't take negative interest rates in order to do that, because people overall seemed to naturally have a significant preference for current consumption (+ve time preference). Another way of putting this is that in aggregate, people wouldn't lend money even risk-free for less than a decent rate of interest (the idea of a 'natural rate of interest').

The hypothesis in the article is that the reason near-zero and even negative interest rates are seemingly required to give the same kind of nudge now is that the underlying preference for current consumption has weakened substantially. The other side of this coin being that people will now happily lend money for a much lower rate because they now value future consumption relatively more than was previously the case (the 'natural rate of interest' has gone down).