You seem to be under the impression that, just because a company is using a common, of the shelf circuit, that they shouldn't try to keep it a secret.
But often, it's not the circuit that they're trying to keep secret. It's that they're keeping secret what circuit they chose to use for an application.
By your argument, software companies shouldn't consider their source code secret. The source code for any given application is, for the most part, just a collection of function calls. All of which are listed in the compiler manual of whatever language they're using.
Another case is the password to your bank, or any other, account. It's just a string of common numbers, characters, and symbols, all of which can be found on the keyboard in front of you. So why keep it a secret?