I can somewhat see the logic.
there are still ppl racing for places so travelling at 200+ km over that patch, add in a heap of smoke and an unknown car, could go bad.
BUT..
considering every fan wants to see that, and that the only time he in front of the main crowd, plus I'm sure he pulled to the side and did it not just doing donuts in the middle, a quiet reminder that it is to be done after turn 1 would be more than enough.
ideally they should be encouraging a bit of showmanship after the finish to keep the human in the sport, every-one is on radios anyhow.
eg more of this...(NSFW comments)
and less PR planned stuff.