I personally think that the 10:10 position (sometimes 10:12 or 10:08) was adopted for pictures of clocks and watches because it is symmetric and looks better. Today the symmetric positions are both aesthetic and customary. Other symmetric hand positions are also used, but not as frequently. Examples include 8:20, 8:18, and 2:50. Reviewing some Seth Thomas clock catalog illustrations, I see a gradually increasing symmetry of the hands as the catalogs progress from 1878 to 1940.
“We always put hands to 10:10 here and in other collections I’m responsible for. The answer is probably quite simply that it looks better, aesthetically and practically, as the clock has a ‘smile’ on its face (not just a marketing gimmick, it really does look better than a ‘down turned mouth’ at 8:20) and, as others have said, because it keeps the hands clear of signatures and other subsidiary dials. I note that not every firm uses that position in their marketing though. Synchronome, for example, appear to depict their dials at 3:00.” – Jonathan Betts
“The opinions I’ve read tend toward ‘framing’ the maker’s name on the clock face. Viz: when the logo is placed above the center, the hands are at 10:10 but when the logo is below the center, the hands are shown at 8:20 framing the maker’s name. Wristwatch advertising follows this trend.” – Les Lesovsky
“Thomas A. Frank wrote: ‘…most manufacturers trademarks are just above the center pipe, and having the hands at 10:10 causes your eye to naturally follow to the trough, thus bringing your view right to the trademark….’ and often the Model name is centered under the center pipe, ruling out any hand more or less straight down (between 5 and 7). Date windows most often are at 9 or 3, and subsidiary seconds usually at 6. For aesthetic reasons you want the two hands neither nearly covering each other nor nearly in a straight line. By default the 10h10 looks pretty good.” – Fortunat Mueller-Maerki