Your sketches have personality, and you have a good idea of balance between curves and straight lines, but when rendered, the above is lost. Perhaps, it may be because of the excessive contrast and too much volume in the details. Try to smooth artistic representations of your product to highlight your ability to design. We can inspire in a car, or a machine, but in the end, we make shoes, and a slight trace of comfort (whether visual), always is good for a shoe.
Greetings.