I reckon that the growth in size has more to do with crash design and safety legislation and also the trend for more interior room.
If you look at modern cars from the front or rear,they are all of a similar strategy-the wheelbase width is something like a third wider than the roof,giving a car a triangular appearance and better stability.
As for crash protection,have you seen the amount of space between the frnit bumper and the engine block?You could almost make a hatch and call it extra luggage space!
I used to have a NK2 GTI and the rad was more or less right behind the bumper and when I had to replace the headlight bulbs on my missus MK4 1.6 recently,I could not figure out how the designers had allowed for so much space behind the bumper but still couldn't get my hand in behind the light unit to get the old bulb out!