A CNC mill that's worth the cast iron it's made from weighs at least 2000 lbs, not to mention it takes a lot of skill to use (workholding, toolholding, setting up feeds and speeds, coolant, etc). It's very easy and very expensive to crash if you don't know what you're doing. A g-code program has to be modified to fit your machine, where the origin is, the dimensions of your rough stock, what tools it expects to have, how much material your machine can hog off.

In contrast, a pretty good 3d printer costs $500, can sit on a table, and the inevitable mistakes you will make while learning how to use it are comparatively cheap.