Earlier quoted context omitted.
Most of Tesla's problems seem related to the other parts of the car: doors, seats, suspension, etc. They are probably the best electric powertrain company in the world, but still not that great at being a car company.
A lot of those parts are from third party suppliers (not that it excuses Tesla completely of course). I watched a video some time ago, where Musk was complaining that the big automotive parts suppliers simply didn't take Tesla seriously, and therefore it led to quality issues, in the video it was the quality of the sun flaps. It's probably due to Tesla shipping much lower volumes, and the big suppliers not being fami…
What makes you think that other automaker aren't using third party suppliers? Borgwarner, Denso, etc... are all third party suppliers that many company uses.
After the recession of 2008, many third party suppliers went bankrupt. There is a consolidation of third party so now many automaker share similar parts among each other.
Even the new Supra, Toyota tested the BMW engine and ask BMW to change some stuff.
It still up to Tesla to test the reliability.