For just a quick little bit of image, I'd say it would take a very large amount of effort and expenses.

The article mentions that the clips are only seconds long for the opening, having not played the game myself I assume it's a montage to establish mood while being narrated over. Filming would be prohibitively expensive for something that could use stock footage instead

I can't say for sure, but I feel like they've taken a similar approach with other CoDs, particularly for historical conflicts like WW2, maybe some footage from Vietnam for a Cold War entry. Usually this doesn't draw ire because it's archive footage of an actual war used to show a 'war is hell' message

The backlash here seems to come from two points. One is the recency of the event which surviving family would still be mourning. The other is that this isn't conflict footage, it's a civil tragedy framed as warfare. This crowd crush was the deadliest mass casualty event Korea had seen in about 30 years

The use of footage where people are killed for the purpose of entertainment is in bad taste on the best of days. CoD has been frequently criticized as being propaganda and while I don't agree that killing pixels turns people into monsters, having actual human deaths alongside it just feels wrong

Aside, the note about conservative politicians urging the prime minister to play this work of fiction as a way of fearmongering to prevent reconciliation with North Korea is truly disgusting

Yea I can't imagine that this isn't intentional. I've not played it so I have no idea if it is relevant but I can imagine it could be impactful if used well. Still, this seems insensitive given it wasn't that long ago.

Edit: Read through the article and seemed like it wasn't necessary at all. The cynical part of me feels like this might've been an intentional marketing move to garner attention through controversy.