Mk1 Golf came out in 1976. The increasing size of the same model of vehicle is more due to brand loyalty retention. They know that in your teens and early 20s,

Mk1 Golf came out in 1976. The increasing size of the same model of vehicle is more due to brand loyalty retention. They know that in your teens and early 20s, you needed a cheap small car. As you get older, you may want more space to do more things, but you really loved your old car. So to keep you as a customer, they increase the size of the new versions of that car. The new car is still the same model as before, but now it meets your changing needs. You will see that the Golf has gotten bigger, but now the Polo has taken over as the small car. The Civic is no longer a small car, and has been replaced by the Fit/Jazz. The Focus has gotten bigger, and the Fiesta has taken over as the small car. The smaller car still exists. Compare a modern Polo to a Mk1 Golf. The Polo will be safer, quieter, more efficient, and probably not that much heavier. Same goes for any car that I mentioned above.