I've been wondering the same thing, it might have to do with the default map effects that are present such as the rain, distant fog outside the map and the lightning all effecting any changes to that sort of thing, hope this helped
If you arent hitting budget, point lights at max distance with no fall off can be pretty effective but I'm not a fan of work arounds for things that should be working properly so take this as you will
Your issue has to do with the inability to generate lighting on the map and/or that 343i does not have fog in that part of the map. So, while you can adjust near and distant fog, depending on the map you may or may not notice it. And unfortunately, we only have 3 maps that allow light generation.