I believe that TWOV was like in China: you are allowed to clear US Immigration and Customs to change planes (and thus mingle with normal departing passengers) without a visa if you’re from a non-visa waiver country, and thus required to leave the country very soon. But enforcement strikes me as quite difficult given that leaving the secure area is no problem, as you’ve pointed out. In ITI, you never enter the US at all and are constrained to areas without an exit to the US until you board your onward flight.