The coin was laundered on several exchanges and not just only exch. OKX DEX and ParaSwap were among and more. Why the regulators do not seize the money from the other two exchanges? Why only exch?
All of them have helped in money laundering if exch is accused. All of them do not require KYC also. Bybit also has DEX called WEB3 on the exchange which does not require KYC.
Those are all DEX aggregators. Trades are routed through many decentralized liquidity sources, which are not under the control of OKX or ParaSwap. They can try to block hackers from using their frontend, but there is no real effective way to completely prevent them from using DEXs.
exch was centralized and could be shut down much easier. They also had full control over the liquidity used to make swaps, so there is a higher degree of liablility. The laundering of Bybit hacked funds is what has gotten most of the headlines but there was much worse people who were allegedly using eXch, and this just made them an easy target for law enforcement.