Why doesn't Halo 5 hit higher fps in 1080p?

If Halo 5 hits 60 frames in 4k resolution, it needs to be able to hit around 100 fps in 1080p. Why aren’t we getting a higher frame rate in 1080p? This will improve the gaming experience. The Xbox one X/s already got an update for 120hz/fps in 1080p… what is the point, if the game can’t use that??? Is 343 planing on raising/doubling Halo 5’s 60fps in 1080p resolution?

FPS is locked at 60 in Halo 5, there are no plans to change this