You don't have to suggest an explanation for this demographic change if you don't want to.

The statistical evidence for a change in the paper you linked and the other papers in the area is extremely weak.

At one end of the scale is very little data that gives an unreliable picture with a high degree of variability, at the other end of the not very long in time scale is somewhat more data that provides a better picture.

To make such a fuss about " this demographic change " indicates a lack of exposure to such statistics.

Why are you attempting to make such a big deal of bad data here?