The problem with 2-4 hour boardgames that require extension rulebooks, launched in the last decade, is that these games are islands. No game can point to another game to offer mental shortcuts in absorbing similar gameplay.
But they absolutely can. Go see Friedemann Freese Copycat, which has zero unique rules: Everything is stolen from a popular game insiders know. Hell, it even has a misprint on purpose, matching a famous misprint! You can teach it in 5 minutes to the right people, just by reference.
The modern, kickstarter heavy 3 hour monstrosity just can't assume that the buyer has played all the games that have the same mechanics they are basically lifting from elsewhere, while only explaining the 2 or 3 places where they are doing anything interesting. But when you go through lives rules explanations among people in industry, half of the rules are really handled by reference, because you know what is going on. With some designers, the rules are almost unnecessary, as the played aids and the graphic design do 90% of the work. I've played that game with a certain designer: He sat there to answer questions, but he didn't even hand us a rulebook, or provide an explanation. Just the components in front of us and 'figure it out', as an experiment on the game's learnability
