Yes, you are very confused indeed. So lets say that someone went trough the trouble of integrating the CG into the game and writing all the dialogue from the videos into the engine, alsongide all the code needed to make it work. What you'll have is just the videos all over again, why would you want that? Why waste energy on that?
They'd be disconnected, since we don't know what happens between the events, where the MC can and can not go, what dialogues are available in the roaming. You wouldn't even be able to roam in the recreated events since we don't know anything outside of what was shown, no door would be interactable, hell, some maps aren't fully visible so we'd have to make up some bullshit. Oh and they'd have to remake the maps too, since not all of them are in the demo, good luck with that.
I'm sure there are other problems as well, but let's stop here. You want all this work just to have the same exact videos except you need to press a button to make the dialogue move forward?