They do. The micro-precision subculture required to (in order):
1. Powder prep your tungsten carbide
2. Form said powder
3. Thermally prepare the resulting slurry using a vacuum forming furnace
4. Finish it with diamond lap grinders, lapping machines and polishing machines
5. Clean it ultrasonically, with solvent, rinse, then dry them.
6. Have the metrology required to test thousands of micron-scale balls a day (a world-beating skill in itself)
7. Build a QA lab that can assure the quality of said balls statistically (you can test them all).
8. And then integrate them via socket assembly
are not just hereditary, but proprietary. And assuming a competitor does manage to achieve the basic ISO 3290 and ASTM F2094 standards, you still need tacit knowledge. Stuff like sintering temperature curves, proper powder grain distribution, polishing chemistry, proper statistical rejection thresholds and a whole lot more.
And that is just the ball. Not the socket, or the ink channels. Making a perfectly spherical 0.5 mm ± 0.0001 mm tungsten carbide ball requires the same techniques used in building micromotors, medical devices, and semiconductor subcomponent manufacturing. Techniques such as high-volume sorting, advanced powder metallurgy, controlled sintering, and precision machines that operate 24-hour shifts without drifting. All operated by modern process engineers who are the spiritual (or actual?) descendants of Swiss watchmakers or the glassmakers of Murano.