who said there was? it's only on the scBTC which is why they will moved to the ZC SC in the first place; to get anonymity.
Here is exmple how to implement
ZC feature over BITCOIN block-chain
scBTC will not move to ZC.
1. We will create new SC over btc-blockchain
2. This new mixerSC can be mined by HMM and (Timestamp server or hashing Oracle)
Now you can use 2x swaps. BTC to mixerBTC and mixerBTC to BTC and you will have BTC mixed with 2 people.
Or you can use 2x 2wp. BTC to mixerBTC and mixerBTC to BTC and you will have BTC mixed with other 2 x N people.
Or you can deposit 10 BTC and withdraw 10 x 1 BTC.
You can do few random transaction in mixerSC to mix them more using mixerZC protocol (it will use same alg. as ZC, but that is all. No other connection to ZC alt-chain).