I don't know why the secrecy exists. (It's probably for a good reason, and this reason is also a secret.)
One very good reason not to reveal these methods in the past was due to requirements of secrecy by e.g. the Nevada Gaming Commission who, in an effort to combat counterfeiting, required that the makers of gaming products like chips, and probably slot machines, roulette wheels, etc... not publicly reveal how these goods were produced. If info was leaked, a company could lose its license
Well the reason you stated at the beginning is absolutely correct
I now stand more educated. Thank you both.
Now, do I (personally) think that is a good reason??? Ehh... everyone can google for themselves if Security Through Obscurity is good or not.
But again, thank you both for unveiling to me one less secret behind manufacturing chips!