The U.S. regulatory system can be quite complex. Often times, it is individual states that have laws against certain specific money transfer service and certain clauses that eventually define DEX or exchange as a money transfer service, then if a DEX or exchange wants to operate in the state they'd have to comply with the laws as a money transfer service on top of AML/KYC, bear in mind that each state have different laws and bereaucratic systems that it is understandable DEXs and exchanges would pull out from the US.

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