They cannot do the materials we need or the size/finish required.
This is where I work:
We have parts that go into the target chamber that are made of pure gold, various aluminum alloys, silicon, beryllium, lead, specific dopants of plastics (which vary from target to target depending on what they are looking for), diamond, lead.... It all depends on what part of the target it is and what they are looking for in the design.
The 3D printed parts we use can be as thin as 150µm and total mass of that specific material per target cannot be more than 74mg.
The gold parts we use are thinner than human hair and all told are less than 7mm diameter and 12mm tall.