3D printing (I started working with it over 20 years ago when it was called stereo lithography) is generally most applicable to fabricating small quantities of complex items. Like any other fabrication technique, there are considerations with respect the materials and the resultant properties of those materials when processed in those ways. Wheel parts are for the most part pretty simple circularly symmetric items and fabricated very rapidly in large quantities and to high specifications. 3D printing of some parts might be useful for prototyping, but I don't see a use for it in production, at least not yet. In the future, who knows?