Sure, ignorance of the law is not an excuse, but contracts are not law. In fact, the law requires a "meeting of the minds" as a required element of a contract. Although, the modern bar for this is extremely low, and courts will judge this based on manifestations of assent.

That being said, Vizio has a high paid legal department and is certainly not ignorant of the fact they ship third-party licensed software. They are simply ignoring it.

Courts would say "look you're professional organization well aware of software licensing landscape and you're using it, so you have agreed"