Earlier quoted context omitted.
Companies often have the monopoly on repair for their products because they don’t make the parts and diagnostic tools available. Yes, they ask money for repair, but there also plenty of repairs they flat out refuse to do. Apple refuses to repair phones with water damage for example. Repairs that repair shops might be happy to do, if they had the access to parts.
How do you repair water damage? Look at the colour of the motherboard and declare it's fine? Besides that, most Apple phones since 2016 or so are water resistant.
Does depend on chips being available and some knowledge on how to diagnose the damages (e.g.: board schematics).
Here's an example of new age Macbook pro's dying from little water ingress (design oversight). And a combination of knowledge and a simple chip can fix your nearly write off Macbook. https://www.youtube.com/watch?v=jahtu1_idVU