Manufacturers typically market the vehicles as energy efficient.
Because they are more energy efficient...
Until now it has been claimed by manufacturers that the vehicles used only a little or almost no fuel when in the electric mode. The studies showed that this was not in fact the case.
Because when in pure electric mode they do use little or no fuel (different cars have different architectures but this is generally so)
But, yes there is a good point buried in there. Europe needs to update rules on efficiency claims. l/100km in gas mode, and electric range gets you pretty far.
It getting worse over time I would think is partially a function of customer mix changing.
You start with early adopters who are more eco conscious and then now entering mainstream, and also people choosing plug-ins for performance purposes.