The inefficiency for cars is a feature. It means drivers will slow down and thus kill less.

https://www.strongtowns.org/journal/2018/1/25/speed-kills-so...

So many of our problems with regard to urbanism are rooted in making things efficient for cars over other users.

Some pedestrians can manage a sloped curb at a crosswalk. Others may have a more difficult time of it.

By contrast, all cars must be able to drive up and down a short slope. They must do so to enter most parking lots, for instance, so performing a similar maneuver at an intersection is no big deal.