This becomes more or less understandable, since the use of a cross-chain bridge, and even into the Ethereum network, everywhere requires paying a fairly large commission. But the OP writes about charging a fee of 0.1% exactly when depositing on the BSC network.
Yes, he deposits from the BSC network, but as you can see from the screenshot, it is clearly stated that it is a cross-chain fee. So KuCoin probably holds USDT tokens only on the Etherium network, hence the fee.