I'm sorry, how do we know this? I saw someone conclude upthread that the timing of the walk was the determining factor (sorry, can't confirm who it was at the moment, you or someone else). But I can think of other potential reasons. Like, maybe it saved shooting time not to put that whole part of the bridge back in place, and the judgment of the director was that it would be adequate for the shot and therefore worth it to move onto other shots more quickly? Or, do we have it documented what the reason was?