Why do they always have to do these shots at night? Is it because the processing to render far away objects in the background is just too much for the engine and they have to compensate by making these things at night so the background behind the characters is black or something close to them?
It's actually the other way around. Night shots are harder to pull off well since the effects of individual light sources are much more pronounced. In this video, they are trying to showcase a number of different light sources, reflections, diffusion which require a dark setting to stand out. Outdoor day shots get most of their "character" from a spot source at infinite distance (parallel rays) which is much less computationally demanding.
