In times of old- all fashion was custom. Apparel had to be designed or sewn by hand. It was only when social disparities started blurring that businesses started selling mass produced apparel; and people started buying it.
The industrial revolution brought standardization to the apparel markets. From gathering raw materials to creating standard fits- the industry has scaled new highs every year. The global fashion industry revenue, circa February 2015, has gone up to USD 1.2 trillion.