The return to the center on it's own is a result of the wheel alignment castor setting
if it set at zero or minus setting ( -1 degree) it has no action requiring it to return to center
To explain how it works --- the angle at which the king pin is set back ( positive degree) lowers the car
when turning a circle , the car is lifted up and loads up the king pin
when you let the wheel go that weight tries to fall down and that is the return to center position action
so to fix that problem , have a wheel alignment done and set at positive degrees ( normally around 1 1/2 degrees)
next problem is when you set with the wheels straight ahead there is no allowance for the camber of the road ( used to allow water run off in the rain) that means that if you position the wheel straight ahead when on flat ground then when driving down the road you will have the wheel slightly off center to allow for the car trying to run off the road from the road camber
it could also mean that if you have had suspension or steering work done that the steering was not centralized when the tie rod ends were adjusted for toe in adjustment and so the box /rack is now set slightly one way
it could also mean that the rear end is out of alignment and the vehicle is running sideways down the road ( crabbing)
the fix is to find yourself an accredited wheel alignment shop and have an alignment done properly starting by aligning the rear wheels first and then the front many will say not necessary but I can assure you that it is vital for tire wear and vehicle handling and if they don't want to do the job properly go somewhere else