You are comparing a two door sports car to a four door sedan. Yes some cars have become larger, but they are also incredibly more safe. The doors are thicker and reinforced to protect you in an accident. The roof is taller and stronger, and the pillars are reinforced steel so you don't get crushed in a rollover.

They still make the Mazda Miata, BMW 1 series, Toyota BRZ, etc. These are all small cars, although I'm not going to research all of their dimensions. The truth is there is a very small minority of people who want cars smaller than that, and it's not profitable to produce them.