Controlling DC Motor with stepper driver
A brushed motor requires a DC voltage to reach full speed and start with full torque then uses it’s armature to self commutate which also results in large BEMF energy released during commutation with only 2 wires to input mux’d to each coil.

A stepper driver always gives 50% duty cycle output as it commutates 1 of 4 phases or full steps to 2 coils and only gives DC when stopped.

Therefore it is incompatible to control velocity with a position control stepper driver.