You would need to rollback safety standards to achieve this.
One of the reasons vehicles are so big now is to allow passengers to survive diagonal and side impacts and rollovers. If it was all front and back collisions then vehicles could get smaller again.
Or add new safety standards targeting people outside the car too (e.g. pedestrians and cyclists, or people in smaller cars) which can and do get crushed by modern monstrosities.
I also feel like modern vehicles lack of visibility causes a lot of accidents that aren't counted.
I have no evidence for either of these claims.
They also require more space for parking that simply places things further away and makes our cities less friendly for pedestrians and cyclists.
Oh, and they are melting glaciers and polluting our environment.