[matthewmacleod]

I've heard this before (and I don't have any reason to doubt your research) but I'm struggling to figure out why it would be the case.

Regulation 1016/2010 (https://eur-lex.europa.eu/eli/reg/2010/1016/oj/eng) is the thing that establishes the various requirements for home dishwashers. It's pretty straightforward (most of the content establishing how efficiency is calculated). It basically just requires the default program to be "suitable to clean normally soiled tableware and that it is the most efficient programme in terms of its combined energy and water consumption for that type of tableware".

I could imagine some issues with how these numbers are calculated that reward "less efficient" devices or something like that, but it's pretty hard to figure out what that could be. Bit of a mystery!