Occam's Razor, the data is bad, and bad in different ways between countries.
>With respect to the raw numbers, underreporting is an enormous problem; differences in age distribution, too, make a very deep cut, and perhaps the models must further calibrate their weightings here.
They go on with the complex speculation about other causes, but obviously bad data is a huge driver of this anamoly. Bad data we can be sure of, the rest is speculative narrative.
The article makes a strong case that bad data only closes the gap partially.