Because war isn't entertainment. It's not "fun." And in physically presenting it as a walk-through attraction, Universal dismissed and trivialized the actual gravity and horror of it. Using war as a real-life "experience," that you're walking through at a theme park, is a tasteless and insensitive decision. Leveraging scenes of war wounded, literally having war nurses taking advantage of those already knocking on death's door because of war it's, is mortifying. They turned war into a "setting," when war is a blood-thirsty behemoth that should never be trifled with.
And I've heard the arguments, comparing movies and video games as entertainment mediums to haunted houses, and they're incorrect. When I watch a movie or a play a video game, the experience doesn't extend beyond the edges of a screen. When I walk into a haunted house, I'm immersed in a setting. We can argue suspension of disbelief, but it doesn't change the principle that Universal turned an ACTUAL war into an attraction that made people jump and laugh and squeal with delight. People who dismissed the crassness of "the WW1 house" because "war isn't like that anymore" are dismissing what war itself is. What experiencing war is. The methods in which wars are fought has changed, but the oppressive terror of it never will. Throwing cut-rate banshees into the trenches implies that war itself, isn't enough.
Never mind how the house affected individuals with combat-related PTSD.
If Universal did a "school shooting" house, people would be tearing them apart. It's the same principle. It's trivializing true horror. I hated the house. Hated the idea and the mere existence of the house. The fact that it was presented less than 12 months after the final WW1 veteran died still horrifies me, and tainted my view of A&D (and Universal) as entities. Part of me hates every single person who thought it was okay to do that. Because war isn't "fun."