Seems logical that the two walls act to funnel people down towards the opening - a 90 degree-wide corner exit is halfway between a 180 degree-wide funnel towards a single door in a wall, and a 0 degree wide corridor that leads to a door.

Likewise the 'obstructed' wall entrance just turns into two corner exits, side-by side (I imagine the scenario doesn't work out well for the individuals caught directly behind the pillar, as the flow past each side of the pillar into each exit zone prevents them from getting into either flow effectively).