They appear on CITES appendix 1, which prohibits the trade in all animals on this appendix by all signatories to CITES. A number of countries that are signatories allow importation if the fish come from CITES certified farms. The fish sold from these farms have microchips implanted and a certificate describing the fish and the chip code, thus authorities could check the origin. The US seemingly keeps to the original agreement and have not relaxed their regulations to allow the importation of farmed aro's.
By far the largest market for Asian aro's is Asia, especially China & Japan where these fish are closely linked to certain cultural beliefs.
I can only think that some form of lobby effort by an industry association would get the US regulations relaxed.