Oh, it's not a secret, it's just "undisclosed"

from here

As surveillance capitalism becomes more and more obvious, the application of old malware tricks in supposedly legit products becomes more and more apparent. No one would buy those eavesdropping IoT devices if they knew about the eavesdropping - which is the same basic approach trojan horse programs take (you wouldn't run it if you knew what it actually did instead or in addition to it's advertised behaviour).

And because no one would buy those eavesdropping IoT devices if they knew about it, technology vendors have to protect their ability to keep that sort of things secret. They're fighting for the right to turn their products into trojan horses.