think about the person who actually draws the bases and stuff doesn't come up with your oc
you yourself have to come up with it
depending on the picrew itself, there is a 0.000001% chance that you will bump into someone who made the SAME EXACT oc as you on their own time
think of it as a drawing base
it's just an outline or concept of what the drawing will look like
however, what makes your final piece different from the base is how you draw it and what details you will add on/ remove from it.