I understand and, grudgingly, accept their explanation. The day/night cycle (which I do think is very important to have when simulating a *real* D&D game) would be disruptive to their current method of story-telling (which is, judging by DOS2, likely to be a really well done, and fairly linear progression of connecting a variety of story way-points.)
That means that they will, likely, simulate some night events to create some variation. But, lets make no mistake, it will be the poor-man's faux night.
I see no reason that they won't be able to pull off an amazing story/game without a persistent day/night cycle... but in as much as it conflicts with their current method of story-telling I hope they realize that it is a self-inflicted wound. With luck, the foundation laid in BG3 will allow them to expand BG4 to include proper day/night cycles (even if it's only through portions of the unfolding adventures.)