Regarding International-to-International transit, USA doesn't have an 'international' hub, much like LHR, or FRA or NRT or HKG, etc. That's because USA is much bigger country than these countries and there tend to be a lot more international-to-international transfer in these places than here in USA. Hence not enough such traffic to make it worthwhile having int'l-to-int'l facility at most international airports.

Of course it's a moot point when the US gov't insists on knowing everyone who is flying into (or even flying through USA's airspace) USA, and thus force everyone to go through I&C, regardless of their final destination. (Before 9/11, such transits could happen without officially entering USA, although it requires extra steps such as being escorted from a special facility to the outgoing gate).