Because it's awesome. That's why I'm playing it. I love the tactical possibilities. Snipers on the second floor shooting across a road at enemies that pop up to shoot at you? Rocket launchers, shot through windows to deal with ambushes. Mines placed in patrol routes, so patrolling enemies don't become a bother, they just become a splatter.
Add up targeted shots, such as to the eyes and appendages. It makes the game feel more fun and functional. I can deal with mutants by shooting their arms and breaking them, so they can't fire at me. Or legs so they're slower and can't chase me as easily.
