Apparently nobody thinks of hiring a press photography consultant to train these extras for the parts they are supposed to play.
There's three problems with that;
Firstly, someone has to recognise there's a need for it.
Secondly, that it's worth spending the money to hire someone for that small benefit. Worth pointing out that once you've trained a supporting artist* for a particular task they're eligible to be paid more for their 'specialist' skill
Thirdly, you assume that the supporting artist is capable of learning the task at all.
Having spent over forty years in TV studios and sets I can assure you that the last item causes the biggest problem. I've watched as a professional on-set photographer has tried to teach an SA how to use a camera with an almost total lack of success many times.
*Supporting artist is the prefered title for those previously called extras.