This always confused me as a child too. Here I am, being told in school about measurements, units, and how important they are, yet the adult world doesn't adhere to that.

Every shoe company has it's own way of measuring a "men's size 10.5", (which has to be different than a women's size 10.5, because ...? tradition?) and now it's even worse. This year I bought new boots and even the same brand didn't have consistent sizes. The more centralization fails, the more I start making it myself, or paying others that are willing to create with quality.