A reason I think KZ's MP has never come close to Halo, CoD, BF is because of numerous reasons....
- Halo has a legacy of SP, story and classic MP. It still has the old school bright colours and sci-fi
- CoD and BF are modern military. The hot setting. One is fast paced with small maps, the other is large scale with vehicles. Both try to be gritty
- KZ goes for the darker, sci-fi setting. It doesn't have anything that really makes it stand out. Gears was a dark shooter too, but it was third person, had cover, and tons of chainsawing blood splatter
So it shows that sci-fi and modern military can both be successful. But something needs to stand out aside from setting.