The point is that a part manufacture has to go through the right channel (ie, get certified, inspected regularly) to have the 'right' to make parts. You wouldn

The point is that a part manufacture has to go through the right channel (ie, get certified, inspected regularly) to have the 'right' to make parts. You wouldn't want parts of questionable quality being put on an airplane, some goes for your car too. Even certified after market parts have their issues too and seem to get worse (in quality) every year.