I don't play war games very typically (I'm much more of a fantasy sort of person), but I get it. I think a lot of war games and war films are similar in a lot of ways to our fantasy and sci-fi narratives in that they both tend to follow similar beats and arcs--great heroes that have to overcome struggles to defeat an enemy and protect their country, etc etc. I think for a lot of people the appeal is the same as Halo or Dragon Age or any other game like that--you want to feel like a strong hero. Is it a little more disconcerting when it's applied to a real world context? Yeah, I think so, but I think people that enjoy more "realistic" scenarios aren't necessarily into the idea of going to war as much as they're not into sci-fi and fantasy as much.

At the very least, my husband is friends with a guy that's reeeeeally into Call of Duty, and for him, from what I can tell, it's mostly about skill. He's competitive and likes to win, so mostly plays online multiplayer. He did try Destiny when it came out, but didn't like it as much, so back to COD he went. On top of it he's also a gun collector (he lives out in a less developed area in the mountains where everybody has horses and things, guns are more common out there), so I think he probably enjoys seeing guns he recognizes modeled in the game as well. (I hate guns, so I don't particularly care for this BUT I get it--I'm similarly excited when I see stuff I'm into portrayed well in games I like, too.)

I also think it's important to note that while Battlefield and COD are mostly just focused on the multiplayer combat, they DO try to address some of that stuff in their singleplayer campaigns (although how successfully they do, I don't know--most people don't really play those games for the story anyway). There's also been a decent amount of "war games" in recent years that have directly tried to address the actual impact on war in people--for example, Valiant Hearts is an adventure game that tries to educate on the history of World War I and attempts to tell very personal stories within the war itself with mixed success (two of the stories are pretty complex and interesting, two of the others rely a little too much on a mustache-twirling villain), and Spec Ops: The Line is heavily inspired by Heart of Darkness (the book that Apocalypse Now is based on) and deals a lot with themes like PTSD.

In the end, I don't know if more unrealistic shooters like Halo or Bioshock Infinite are really all that different from COD or Battlefield outside of window dressing. I am a little uncomfortable with the ones that seem to make light of war, and I'm against glorifying it, but sci-fi games tend to kinda go out of their way to portray the "evil" aliens you're fighting in a way similar to how propaganda might portray enemies in a war (They're part of a cult! They're different from us! They want to kill us all, so we have to kill them first!) and even when Bioshock Infinite tried to have a message about extremism it was diluted by the fact that you just kill wave after wave of nameless soldiers, some of which are just doing their jobs or protecting themselves.

I dunno, I'm rambling at this point.