The three pillars of expansions

Container has been hitting the table every week since I got my copy, iterating with the various expansion modules to test my gut reaction that anything added on to the original game actually detracts from it. It got me thinking, we all know there's games that needed their expansion (looking at you, Rebellion), but what makes a game more or less expansion-friendly? There's the obvious negative response to the base game disincentivizing it in the first place, we're never getting more Founders of Gloomhaven, but what makes us look at a great game and say “that's it, no more.”? I've come to the conclusion that a game's got to check a few boxes for more content to make sense to me.