So I work in manufacturing. On one of our systems, we recently upgraded the fleet to a $10k computer with a 22nm processor running RHEL 7 supplied by the system vendor. We had all of the install files and could have bought a $2k computer and gone through an extended install and qualification process, and closing the door to some support from our vendor, but we didn’t. We paid the extra $8k for a guarantee that it would just work and that we could get the exact same computer for years to come.
I see these high prices for what appear to be commodity items in a similar light. You are paying for a certain amount of comfort that the sling will just work. Amazon is not going to care if the sling, which might be a cheap knock-off, rips apart while you’re walking and unseats your unhealed bone.