Well, obviously Big Money is not why we play Dominion. Every kingdom card tries to steer us away from pure BM, simply because it's not what the game is about. If pure BM without kingdom cards was a good tstrategy relatively often, Dominion's design as a game with kingdom piles had to be fundamentally flawed. It's basically a savety net, design wise: If, against the odds, the combination of kingdom cards is so unfitting that it becomes impossible to effectively play a combination of them, there's always Big Money. What makes this net more agreeable is that, even in such cases, kingdom cards will almost always add something, even if you limit yourself to very few of them. Heck, even opening Chancellor/Silver is strictly better than Silver/Silver if you will ignore all other kingdom cards anyhow (edge case: terminal collision with involuntarily gained terminals because of attacks). I get where the idea of BM as "default" comes from, and maybe it's just nomenclature, but i think "default" communicates "usual", which is not what i'd call BM.