Combine organized with expansive and you get cheap courthouses, lighthouses, granaries and harbors. Great for large scale early expansion. Also it matches up with rome's early UU which everyone knows is quite powerful. Plus high health and the ability to support whatever civics you want without feeling the pinch. Mainly I think people don't look at the cheap building you get. They only see the global benefits. After an early expansion getting your courthouses up is crucial. You can favor coastlines early on with the cheap lighthouses, and harbors. This helps because you don't need to build as many tile improvments and saving your workers for the resources.
Not to say other traits aren't powerful, but to me these two combined with their UU just line up at the right place in the right time.
If I had to pick another pair it would be financial/spiritual. You can get big $$ from financial and spiritual makes it easy to pop back to War civics if the need arises.
-JG