The offspring of Abraham’s other sons were not used to bless humankind. The seed of blessing was to be through Isaac alone.
فَبِحَسَبِ ٱلْكِتَابِ ٱلْمُقَدَّسِ ،‏ لَا يُبَارَكُ ٱلْجِنْسُ ٱلْبَشَرِيُّ إِلَّا بِوَاسِطَةِ ٱلنَّسْلِ ٱلَّذِي تَحَدَّرَ مِنْ إِسْحَاقَ بْنِ إِبْرَاهِيمَ .‏