Because the headers are only in breadboard. The motor driver will fit over the connectors but not connect as there are no connectors on the headers in breadboard that it connects to (and the driver in core parts is too large to fit in the board in schematic.) If you change the grid size in breadboard to 0.05in you can correctly align the part like this
but in schematic the part in core parts is too large to easily fit within the expansion board
Peter