The single clock owner doesn't have to be especially lucky. Imagine if they had a clock that was two minutes fast and the dual clock owner had one that was mere

The single clock owner doesn't have to be especially lucky. Imagine if they had a clock that was two minutes fast and the dual clock owner had one that was merely a minute fast and the other was ten minutes slow. The average would be less accurate, despite owning the most accurate clock. Two clocks just don't work for statistical analysis (three clocks are unlikely to help either). Also, the single clock owner is justified in believing that they have the correct time as there's nothing to suggest that they could be wrong. Two clocks introduces doubt where there was none before. Rather than using "justified" true belief, humans tend to go for the easier option and would be more likely to go to the person with just one clock, until they find someone with enough clocks and clout to point out the likely correct time.