Why do we use low resistance cables to minimize power losses?
You are assuming cables and load to be one "unit". But this does not make sense in this case.  

Typically, your load requires a specific power and for that it needs some specific current (calcualted by Ohms Law). This current now creates additional losses in the cables and these losses are lower when the resistance is smaller.

Take, for example, a 500 W computer power supply. When the computer requires 500 W, the PSU will deliver this power - independent from the input voltage, at least over some specified input voltage range. But a resistance in the cable creates a voltage drop, so the power supply needs a higher current to deliver the 500 W. So you get high losses in the cable.