Since I don't know why and your question forces me to guess, I doubt they gave much thought to having their fraudulent recording scrutinized so closely. I don't know how long it was widely known that the recording wasn't genuine. As for as I know, it still isn't widely known to be a recreation. I would wager most people, having heard it so many times, still think it is genuine. I'm not sure when I learned it wasn't, but I think it was within the past 10 years, probably less.
People might not think it is a big deal to have manufactured the recording and presented it as if it were the real deal, such practices open the door to fake news. This was demonstrated by Duncan when he posted what was supposedly an undercover recording of someone talking about a plot to kill JFK a week earlier in Miami, when in fact it is a recording made of actors reading from a script. There's no way that can be considered evidence of an earlier plot to kill JFK. There is a reason there is a strict code of journalism ethics that says news organizations don't create or stage events. It opens the door to all sorts of chicanery. Even something as seemingly innocent as Cokie Roberts doing a supposed on sight report while wearing an overcoat in front of a picture of the Capitol crosses that line. In recent decades, news organizations have seemed more than willing to cross that line to push an agenda.
When they put stuff like this together, they do Not just arbitrarily chose a 16 second gap. There's some sort of basis for using the "16" seconds.
With respect to JFK assassination plots, the Chicago, and Florida planned assassinations are documented. And those involved a tall building.
