Not a litre, not a pint, not a tidy fraction of anything obvious. Three competing explanations, and all three probably played a part.

Same chalk, same grapes, same method as Champagne — just a few hundred miles north, and only ripening properly since the climate warmed up.

You would not call all red wine Burgundy. Stop calling all sparkling wine Champagne — six styles, one gas, six genuinely different drinks.