It's a cyclocross racing thing. Generally they're never used outside of CX racing because nobody rides with their hands in that position unless they are climbing a steep grade and are positioning their body for best respiration and core muscle engagement. Going uphill slowly at very high effort rarely generates a need for emergent brake use unless you are in a very dense pack of people. Even then, hands on the hoods/shifters would result in more control. They are also a secondary to a crash broke brake lever.

IOW: those levers outside of that specialty use are a redundant waste of space & as such most people remove them.