Spindles, motors, circuit boards with components on them and bearings, slides and so on are all multi material or very complex processes usually only doable if you produce a lot of something in one go.

Just try to think about what it would take to print something as trivial as lacquered copper wire for stepper motor windings or a circuit board with a reasonable level of integration.

And the biggest issue with that prediction is that there is no gain from it: printing the non-commodity parts is the whole trick to efficient 3D printing, mass produced parts will have incredible accuracy and very low pricing so use them when you can and 3D print the remainder.