What we really have here is a company that wanted to make the best game they could. It's The Witcher 3: Wild Hunt, their first frontier into the open world genre. They dive in and feel confident about what they're making, release a trailer then, in the following months, they realize that their tech just doesn't scale that large. The current-gen consoles (the next-gen consoles) just won't be able to handle what we're doing.
At that moment there was a fork in the road. Path A, and path B.
Path A: "Hi Witcher 3 fans. Due to circumstances we were naive of Witcher 3 is undergoing an overhaul in terms of technology. As such, although we assure we will make the best game and the best looking game we are capable of, it is possible that the game will not look the same as the 2013 trailer. There are features in the aforementioned demo that just aren't tenable on current technology, console or PC. We will do our best to remove footage from the 2013 trailer from our promotional materials now and going into the future. The Witcher 3 will still be our most ambitious product, and we are still aiming for it to be the best looking game CDPR ever makes, and the best that you will have ever seen. Thank you"
Path B (exaggerated for the purposes of comedy): "Downgrade!? Hah, downgrade? I laugh in your face, "downgrade". The Witcher 3 won't look as good as the 2013 trailer. It will look better! Far better! We have a new shader, and it's better! It will look so good that we don't want to ruin it by showing you Ultra settings now and allowing you the opportunity to compare the graphics, you'll just have to believe our word and wait until launch. But trust us it will look every bit as good as the 2013 trailer and then some. Seriously."
They took path B. In short, they fucked up. They lied.