That is very rational. Each 9 in uptime or quality represents expense. The expense of moving to the next level up can't always be "shift left", but instead done at the point in the process where money can be applied.
Lets say you have a process that goes right at a minimum of 20% of the time for cost of 100. The manufacturer can add QA that makes the cost 120. Is it better to trust the manufacturer at the cost of +20? Or is it better to do your own QA for 20 and gain any correct pieces above the 20%?