They are largely the same because the alternatives fail in various ways: they fail to finance their campaigns, i.e. they fail to get aristocratic backing, and/o

They are largely the same because the alternatives fail in various ways: they fail to finance their campaigns, i.e. they fail to get aristocratic backing, and/or they fail to appeal to the tiny minority of most motivated participants, i.e. primary voters. Also, the two parties have conspired to put in all kinds of barriers, at the state and local level, to make it difficult to unseat their primacy. But to say they just aren't all that different, ignoring the effect of consistency over time, is like suggesting the pressure differential above and below an airfoil isn't that different. It is true, but it's not a complete answer either.