I would never check a bag on a hidden city flight.

Flying through the US for any international flight you always have to collect your bags, clear customs and immigration, then re-check them.

The US does not have the concept of international transit lounges like other countries do, where you can get off plane 1 and sit in a room that is not technically inside the country (so you don't clear customs or immigration), then just get on plane 2 and go to another country.

I suspect there would be cases where it's cheaper to book a connecting flight through the US to some other country (or US city) and just get off at your first stop.

Makes sense, given the massive security theater in the US and the fact that it's so off the beaten path of the rest of the world that most flights probably don't just "transit" through the US on the way to somewhere else.

I was in South America for a year, and tons of Europeans had a nightmare flying to South America because the majority of flights "transited" the US, so they had to get a visa and all that for a 1 hour layover each way.