Why do commercial chocolate/cocoa products often contain fat-reduced cocoa? I've noticed that many 'chocolate' or 'cocoa' products, such as chocolate cake, chocolate milk and cocoa cereal contain fat-reduced cocoa powder rather than normal full-fat cocoa powder.

Often the products also contain added fat, so in these cases presumably fat-reduced cocoa powder isn't used in order to reduce the product's overall fat content.

Is fat reduced cocoa powder cheaper than full-fat cocoa powder? Or perhaps the fat in cocoa powder behaves differently from other fat, necessitating its replacement?
Without getting arrested for loitering in the baking aisle of my local supermarket comparing weights, ingredients and prices, to me it is all down to price and processing method. The low starch, natural fat product performs better according to Cooks Illustrated.

Higher natural fat = premium product = better taste. 

References:

Alice Medrich: https://food52.com/blog/9521-how-to-identify-good-cocoa-powder-and-not-so-good

Cooks illustrated: https://www.cooksillustrated.com/articles/663-which-cocoa-powder-should-you-buy