There are good answers, like John is an expert in the specific technology you're using and he was hired through a meet-up you sponsor; there are bad answers, like John has found a way to game the ticket system; and there are debatable answers, like John's team has a high support burden which he never helps with. If you insist on seeing him as a 10x developer through innate skill or divine fiat, then you're not going to look for the root cause of why he's doing more work than everyone else.
Once you define it as an engineer who ships 10x as much business impact (ships fewer bugs, builds the right features, etc), it’s less contested but also less glamorous and harder to measure. In fact you start to develop an inkling that such people may not even be the same coders you once idolized.