1. Small production batches,
2. Low typical usage - most RR owners do not use it to commute on a daily basis, hence do not face high reliability requirements,
3. The ability of the typical buyer to overspend on maintenance, whether preemptively or on-demand.
Check this out where the clock spring is the same as a bmw part and just the knobs are fancier (and swappable!):
https://www.reddit.com/r/Justrolledintotheshop/comments/18m5...
Which RR would do to avoid the obvious problem, only after a supplier has been verified to be sending only the highest quality product, would they ease off.
The simplest thing is that the supplier charges double or triple the unit price such that they can accept half the parts failing inspection and getting sent back.
Or another way: you an QC a bolt to death, but that doesn't tell you if it's undersized for the design.
Do you not know how car manufacturing works?
Anyways you don't have to take the quality of RR parts on my word if you still think it's impossible, just go a showroom and inspect it yourself.
Even a high-resource prototyping program can only go so far with scenarios like - wear and tear/part fatigue, adverse environmental conditions, local peculiarities (e.g. regulatory requirements for uncommon configurations), unintended but common maintenance mistakes etc.
For example, a Fiat car my family owned suffered a cascade drivetrain failure after about 9 years on the road. I don't think a prototyping program could have captured that ahead of time.
The fact that the showroom RR parts look fine only indicates that the parts are ok immediately after manufacturing; it does not promise they'll work fine after several years even if treated will.
Which is why automakers typically recommends a maintenance schedule that catches the vast majority of potential failures before they occur on the road.
How does this, or anecdotes of your family's Fiat, relate to engineering and verification practices of parts coming in from suppliers?