If you design in something which is later not used, you don't populate that part of the circuit board. Not unless you're intending to use it later, anyway. Components cost money.
A software equivalent would be "we had plans to offer an integrated backup system but that didn't happen, although we still upload your contacts list and the contents of your SMSes to our servers."
If you design in something which is later
not used, you don't populate that part of
the circuit board.
I think there is no doubt they intended to start using it later, because they did.
As long as the microphone never recorded anything, they're no legal downside to including it and not documenting it. There could be a slim but potential issue with advertising a microphone that the customer can never use.
The response to this incident is showing that that view is changing though.
Nintendo released multiple generations of consoles in the US with expansion ports for peripherals that ended up not making market sense to bring to the US.