I’m not here to defend apple, I’m a very satisfied user
But Where do you get this information ?
IFixit has do it yourself tutorials to replace an iPhone battery…
This is from 2016
So there are authorized (ie quality validated) third parties that can work on your apple devices…
As to wether why anyone would want a non qualified technicians putting non qualified parts into a device I much depend on is beyond me… but may be you see it differently.