You have them. You can't really use them. Such is the way of the grind towards actual gameplay in the modern age.
Meanwhile, Futuremark had a fully 3D space FPS back in 2008, called Shattered Horizon. It never really took off, but if you imagine those duels in Ender's Game in zero G, it was like that except you could thrust in any direction. Such an untapped dimension of gameplay, up and down were all relative and you were never really safe behind cover.
Speaking of 3D battles nobody is playing I want people to play Rogue Squadron again. It’s all rebel vs imperial fighter battles it’s so much fun. But it’s totally empty.