It's all in the name of cheapness...If you are manufacturing radiators, you need a stock of tops and bottoms, and when a manufacturer of cars requires a given amount of cooling, you fit the depth of matrix to the stock top and bottom that fits the model in question, and bob's your uncle...a "glue'n'fit radiator...nothing sophisticated about it...and another corner cut to bring the model home to the promised price...I worked for a main dealer in the '70's dealing with price cutting problems...Headaches anonymous(e)

Cheers
Helen