I think most of it has already been mentioned.
At the moment the US is relatively undeveloped as a market, so they're buying the kind of cars that we would generally reject - heavy accident, tampered odometers, rusty etc. Plenty of JDM wood-ducks for the exporters to burn before they start to wise up over there. With the exchange rate taking a dive, cars ex-Aus are looking more and more attractive, but the US would rather buy crap and keep prices landed in the US under $20K there than worry about quality.
The market will start to develop though, and as time goes on, buyers will be looking for clean cars globally, and paying big dollars for them.
It's the same phenomenon that has seen virtually every 240K coupe disappear from Australia, mostly to the UAE.
Most collectible sports cars go through a depreciation cycle, then rise again. In Japan, prices of clean 32s started climbing about 7-8 years ago. Clean series 3 R33s have also been rising for a while, and R34s hit the bottom of their cycle about 5 years ago too.
Australia's cycle is a little longer, so we're only starting to see the rises occurring now (although demand from the US is speeding that process up). If you're buying locally, look for clean late model R33s and clean, genuine km R34s as they're money in the bank as far as I'm concerned.
I'm hoping to send my N1 to the US in 2026, in the hope it will fund my retirement