I have been having a blast reading the manuals for board games I've found on Tabletop Simulator. I've only played one game of Gloomhaven so far, but have read the rules for Star Wars: X-Wing, Star Wars: Armada, Wingspan, Talisman and Twilight Imperium IV as well, with several more manuals for games I have already subscribed to to go. It's like it's my birthday!
I think this is probably one of the main reasons. I can't even imagine what the first No Man's Sky manual would have looked like, but it wouldn't be helpful at all for the current iteration of the game. (See also Minecraft.)