They don't want you to repair devices with used parts or 3rd party parts, because then they don't make a profit.
And that you pay almost the same price as repairing it at the apple store.
The self repair program is just a marketing scam.
Last time I went to an Apple Store I asked about repairing the power button of a (then) three year old device and the answer was “buy a new one, your device is too old”. So, I put in doubt that they favor repairs, as in the end new devices make more money.
Needless to say, my device still works perfectly (except for the button) two years after that comment, and probably will do so for several years more.
Apple: "That would be $890 to repair, maybe we should talk about helping you get into a new Mac?"
Then (doh!) I realized what you meant...
This is why when you take your laptop into the store, they don't offer to just desolder the bad chip, and replace it. They don't want to take the time or money to train their store in doing these repairs. There's a lot that can go wrong and its easier to just make the policy to swap the entire component - the whole logic board. It's a lot quicker to do, it's a lot quicker to train, it's a lot lower risk in terms of chemical exposure, proper-ventilation, and materials disposal. If they take the entire bad motherboard, they can box them all up and ship them in bulk.