I really don't know how to make this any simpler for you to grasp. I'll try.

I have a UTXO of 0.5 BTC.

I make a transaction sending 0.2 BTC to Wasabi, and 0.3 BTC to a change address.

After Wasabi have thoroughly spied on the 0.2 BTC I sent and received permission from their blockchain analysis buddies, I am hopefully granted permission to coinjoin it. Ignoring Wasabi fees and transaction fees for the sake of simplicity, I now have a coinjoined output of 0.2 BTC.

I then combine this 0.2 BTC output with my original 0.3 BTC in the change address.

There is nothing Wasabi, or Samourai, or JoinMarket, or anyone else for that matter, can do to stop me from doing this. Samourai give the transaction a specific name and segregate the change in to a different account to help prevent the user from making this error, but there is nothing they can do to stop it entirely. Wasabi also cannot stop it, but they choose just to ignore it instead since they don't actually care about their users' privacy in the first place.