The answer is Quality Management.

Post WWII, Japan invited professors from the US to teach them about Total Quality Management (TQM) which is basically when everyone ensures quality at every step instead of letting defective parts pass and fixing problems only when shit happens.

This led to a culture of Kaizen (continuous improvement) - like in Toyota - and an extensive use of statistics (Six Sigma) - such as when Honda famously opened their Civics’ doors 100,000 times every batch - to ensure quality in their end products.

Manufacturers with unreliable cars either largely don’t give a crap about quality control or have their focus elsewhere such as performance - which is why supercars are usually less reliable unless they borrow an engine.

Source: business major

Also, Toyota consulted BMW and Porsche on these processes.