In the past, it has been very costly to get accurate sizing info and then custom make the shoes or boots, which is why it’s so rare. Especially since certain styles (mostly women’s styles) require specialized equipment and can’t be made using simple hand tools by a cobbler.
Until now. Thanks to the recent advent of 3D image capture technology that can now be programmed into a smartphone app, you can now get highly accurate sizing at a tiny fraction of the cost.
Then, using existing software, equipment and manufacturing techniques, you can mass produce custom sized shoes and boots quickly, affordably, and profitably!