I agree with you 100% for websites and it is no coincidence that this Mastodon instance is light mode.
But weirdly I go into reverse when I go into SSH/Console mode. It has to be white text on black background with flashes of green for host/usernames. Maybe a throwback to pre-gui early PCs and VDUs when black background was de rigeur.
Maybe we are locked in our brains to reading newspapers, magazines and books. I imagine that many who go dark may come from gaming with less baggage from consuming printed paper text.