It's only marginally habitable -- the average temperature exceeds 100F for six months of the year, it receives minimal rainfall, and has no access to water, fresh or salt.

The primary reason that it remains unclaimed (despite the dispute between Egypt and Sudan) is its inhospitable climate. Several groups have attempted to claim the territory but, importantly, none of them actually moved there and tried to improve the land or protect the border.

I stumbled upon this, as this region leaves a significant timezone gap, when the earth is divided into polygons of timezones.