The reason why you can get any device fixed is the availability of parts, yes. But also all of the highly specialized tools available combined with the skill of people in there.
Even if someone in the US could get the exact same parts, they wouldn't be as able to fix the devices due to the lack of devices and necessary skills. This is also the reason why most electronics are made there, it's a staggering concentration of skilled electronics workers.
The reason why you can get any device fixed is the availability of parts, yes. But also all of the highly specialized tools available combined with the skill of people in there.
Even if someone in the US could get the exact same parts, they wouldn't be as able to fix the devices due to the lack of devices and necessary skills. This is also the reason why most electronics are made there, it's a staggering concentration of skilled electronics workers.
[1] https://www.youtube.com/channel/UCO8DQrSp5yEP937qNqTooOw