There was minute and a half of 3rd person cutscenes in that 48 minute demo, rest of it was first person.
Yes. Again, this is all speculation and based on no proof at all, but I suspect that what happened is that there were relatively few third person cutscenes in the game and they were having problems with the facial animations of the player character in those and they basically went "well, we only have a few of them in the game anyway, so screw it, lets just remove all of them".
Of course, its possible that the decision to have no third person cutscenes was made before the 2018 demo was released, but then why on earth would they show them in the demo at all? Showing something in a gameplay demo that you know is not going to be in the actual game is called lying. Of course, game companies do that all the time, but still, thats the kind of thing that is going to bite you in the ass later.