They're no longer a pure dex relying solely on independent liquidity; they also act as an aggregator to offer the "best" rates. They have multiple exchange routes that can sometimes be heavily censored, so not all exchanges are allowed if users choose the wrong route. One of X's stories:
https://x.com/i/status/2022242446613139782It is a common misconception that THORchain and THORSwap are the same thing, but they are independent. THORchain was originally designed without an official frontend and allowed anybody to launch their own interface and collect affiliate fees. Thorswap began as a UI for THORchain, but over time they have become an aggregator of different cross-chain protocols.
THORchain remains an autonomous protocol that relies on its own liquidity providers and without KYC/AML enforcement. Aggregators like Thorswap and Trust Wallet can tap into that liquidity if their algorithm determines they have the best rate.