For some kinds of motors, principally motors with terminal-based connections, basic wiring is self evident. The terminal board itself usually has markings that indicate where line one and line two are to be connected. But what if you need to reverse that motor, use a different (but available) voltage setting, or have a motor that has nothing more than a bunch of color-coded or numbered leads coming out of it?
Magnetically soft materials, however, tend to be more expensive. The motor manufacturer must find that proper blend of just enough magnetically soft material to do the work required without putting too big a dent in the customer wallet.