Yea, OP if you're just searching "BKK-CLT" and expecting aa.com to return any and all available flights then you're doing it very wrong

Unless you just happen to get win-the-lottery lucky with your dates then you'll most likely never find anything given the current state of partner availability.

As mentioned above you need to search bit by bit and piece it together one flight at a time. Research what partners fly into what cities in the US. Search the long haul segments first, if you find something put it on hold then search from BKK to the Asia gateway (and from the US gateway to CLT or wherever).

If you're willing to spend a few more miles then you can go via the Middle East on QR, EY, or RJ as guv mentioned, but you have to break up the search into say BKK-DOH + DOH-BOS/PHL/ORD/etc. as if you just search BKK-ORD then aa.com will not return any QR results since it can't be priced as a single award.