According to the New York Times, the main reason is quite simple and obvious: aesthetics. There are a number of visual advantages to having the hands set at the 10:10 positions.
One is that the hands are kept from overlapping. Having them on both sides of the watch face ensures that the hands themselves are visible and can be appreciated.
The position also allows the hands to look nice on the face of the timepiece. The 10:10 position is symmetrical, and the human brain tends to appreciate symmetry and orderliness.
Some product photos of watches foun
Some product photos of watches foun
Another reason is that key details on the face of the watch or clock usually remain visible at 10:10. The logo of the manufacturer is usually found under the 12, and sometimes next to the 3-, 6-, and 9-o’-clock positions. Logos found under the 12 are nicely framed by 10:10 hands.
Finally, the 10:10 hands look “happy” due to the fact that the hands look like a smile (or like a “V” as in “victory”). The NYTimes reports that Timex used to use the time 8:20 in their product photos, but eventually decided to turn that “frown” upside-down.