I suspect that the lack of butter in croissants is simply because the cost of margarine is very slightly lower than butter and thus the profit on those with margarine is higher. A half percent reduction in material cost might be a two percent increase in profits.

And as long as a substantial fraction of the customers keep buying the inferior product there will be no incentive for the introduction or wider marketing of the better one.

So stop buying crap food and tell all your family and friends to do the same.

A croissant without butter is not really a croissant in my opinion and as far as I can tell they all have butter here (Norway), here's an example: https://translate.google.com/translate?sl=auto&tl=en&u=https... (they come from the Netherlands).