It's been that way basically since indirect fire took over as the big killer, IIRC around WWI, maybe somewhat earlier. Odds of seeing the thing or person that makes you a casualty plummeted some time around then. Less a series of deadly contests and more bunch of very one-sided slaughters, and you just hope you're not in the herd being slaughtered.
Soldiering has mostly been wandering and/or sitting around and then suddenly something happens that you didn't even see coming, and it either gets you or not and there isn't much you can do about it, for some time. Pitched firefights with an enemy you can at least kinda see and face and actively resist or guard against do happen, but they're not what either side is trying to do most of the time. At least in wars between somewhat-modern militaries. I think militaries/governments like to downplay the degree to which that's true, probably because it'd hurt recruitment numbers, but now we get cell phone and drone videos straight from the front.
Of course, before antibiotics and modern medicine, you were probably gonna be killed by disease before an enemy could hurt you (and if the enemy did hurt you... yeah, good chance it's still disease that strikes the killing blow). That was (one part of) the unromantic reality of war in prior centuries.