Maybe part of the job of these specific officers is outreach, and they think staging a silly photo contributes to that. Or they could be waiting for something/someone else, and thought this was more interesting than just standing around talking about the weather. Or maybe they were indeed doing this after or before work, or while not on the clock for other reasons. Truth is, you don't know any more than I do. And to be honest? Even if they had no excuse, how much pay do you really think they would have collected in the five minutes it took them to stage the shot?

(Sorry, but it annoys me when people expect perfect efficiency from others. Hardly anyone is actually doing work every single second when they're at work, and if you are, I'd advise you to ease off before you burn out. That applies to cops as well as everyone else.)