Can't the attacker simply trace the non-dust UTXOs of that address?
Of course, but they can do that without sending dust to it as well.
The point of a dusting attack is making sure the wallet now has many UTXOs assigned to the same address, to increase the chances that one of them gets spent simultaneously with other addresses that wallet has. The attacker then gets to observe what those other addresses are and infer that they're part of the same wallet as the dusted address.
They can make this infererence always, even without dusting it. But dusting it causes the wallet to have more UTXOs to pick from, making it reveal more if those dust UTXOs get spent in many distinct transactions. And in this case, not spending the dust does indeed thwart the attack: the attacker does not get to see more than they would without dusting.