Why is there a part of the Sacred House (Kaaba) that is empty of worshippers?

The Hijr Ismail (Al-Hateem) is left empty of worshipers during obligatory prayers due to the difference of opinion among scholars regarding the permissibility of performing them inside the Kaaba. This is because the Prophet, peace and blessings be upon him, only performed supererogatory (nafila) prayers inside it. It is occupied with supererogatory prayers outside the times of obligatory prayers. It was named Hijr (enclosure) and Hateem (demolished/broken) because when the Quraish rebuilt the Kaaba, they did not have enough funds to complete it according to the foundations of Ibrahim, so they cut off this part and enclosed it, as it is a part of the Kaaba around which circumambulation must be performed from behind it.