Why don't dentists order restorative implant parts online?

I am curious on why many dentists do not order restorative components online. Many of the implant manufacturers offer either discounted rates or free shipping, however that does not seem to be enough. Is it the confusion of the parts needed, poor e-commerce sites with the implant manufacturer, they don't do enough implant cases. Curious on what others thought about online restorative implant ordering, and why it is not used.