What is your proof they don't have a duplicate key that also unlocks it? A firm handshake from Tim?
If they say they don't, and they do, then that's fraud, and they could be held liable for any damages that result. And, if word got out that they were defrauding customers, that would result in serious reputational damage to Apple (who uses their security practices as an industry differentiator) and possibly a significant customer shift away from them. They don't want that.
You should watch the whole BlackHat talk (from 2016!) from Apple's Head of Security Engineering and Architecture, but especially this part:
https://www.youtube.com/watch?v=BLGFriOKz6U&t=1993s