Have you ever gone to a local hardware store to have a key made, only to have that key not work? There is a reason why locksmiths can be trusted with making perfect copy’s. The depth of the cuts in your keys are specific down to the thousandth of an inch, and key machines have to be regularly calibrated to ensure that it cuts the perfect depth. Not only do the machines go out of calibration on a regular basis, but they should also be calibrated for every different type of key it cuts. Hardware store machines are rarely calibrated and certainly not adjusted for the different keys they cut. A ford key cuts very different than a house key, and if the machine is off a few thousandths of an inch, the keys simply will not work.
The second reason is the key quality. Most smiths carry solid brass keys, not pot metal, not plated, not tin, solid brass. These keys last longer, wear down less, and have a lesser chance of breaking.