Bass speakers are not directional. Near a wall, air cannot displace, only the pressure can vary. When standing waves form in a room, the places near walls are nodes with respect to displacement. That makes them antinodes for pressure. A speaker next to a wall is in a pressure antinode for standing waves of multiple frequencies, an ideal position for driving those waves.

Corners maximize this effect. A speaker in a corner where two walls and the floor meet is in an ideal position to drive standing waves along three axes.

I suspect, turning the driver toward the wall helps it get closer to the wall, and to create pressure in that space.