What's the deal with night mode?

At the risk of sounding like a Jerry Seinfeld bit, what is the deal with night mode? I was in a meeting today where somebody touted night mode in a tool as a Really Good Thing™ and I’m perplexed.

I’m not perplexed about what night mode (or dark mode) is. I might be a bit dense, but not quite that dense.

I’ve experimented with tons of themes, etc., over the years on Linux desktop environments. Mostly I tend to drift back to light themes because the dark ones feel a bit oppressive.

What perplexes me is that the mode is so popular it rates product announcements and has so many zealous proponents. What am I missing?