a_g123:
if a low cost L293D part burns out for some reason, it can be swapped with a new piece at a lower cost.
Or, you could adopt a more state-of-the-art approach to your design, and prevent a failure by doing it right in the first place.
And anyway, the cost of a repair isn't limited to the cost of the failed part. It must include the opportunity cost of the plant being out of action, and possibly even penalties for late delivery. Not to mention the risk of injury if a motor and whatever's attached to it is un-controlled.