There are various reasons why the Ummayads ,Abbasids and their predecessors haven't inserted their dominance and the sphere influence in HOA during the expansion of Islam which the conquest of vast territories had a major impact as far as North Africa , Andalusia(present day Spain) and the Far East Indus valley (India) .
If we review upon history there were historical links , mutual ties between kingdoms and chiefdoms and merchants buying slaves, ivory , frankincense, spices and various resources to make jewellery from East Africa before the birth of Islam.
And even wars and Invasions had took place which date back a thousands of years.
After the birth of Islam,the long term conquest of Makkah and the Kabbah
The entire Arabian Peninsula were united under the banner of Islam, laying the foundation of subsequent Islamic expansion.
Entire empires and kingdoms existing for centuries crumbled as their older wise chiefs saw their demise unfolded and for a time mused themselves into seeming oblivion.
stretches of land incorporated by the unstoppable forces, we often question what were reasons not to invade the Coptic believers of Abbysina, when the forces plundered and waged wars against the Byzantines, Egyptian Copts, the Persian Sasanian Empire was it because during the reign of Negash and his generous hospitality for the fleeing Muslims of Makkah ?
It's hypothetical to say that , when Bab Al Mandab is only few stretches of kilometres away from Ras Menheli in Yemen , it could be easily flooded with fleets of troops in days time as the Abbysinians once conquered Southern Arabia generations ago.
But there are feasible explanations why it didn't happen.
If it had happened we would have been a bastardised people
The scarcity of the region and hostile nature of the pre indigenous inhabitants made it difficult to expand their dominance , they have asserted to spread the word of Islam instead for their own gains , to solely have an ally in Islam to curb the Christian giant .
if history was altered in timeline unfamiliar to the present and asserting dominance in HOA had actually happened , then history would have changed drastically
somalis were monotheistic at the time and they could have been at risk of enslavement just like their Galla counterparts if it weren't for their embracement of Islam.
zeila is the first place were Somalis converted from Waaq to Islam, the first tribe embraced and so did the neighbouring tribes, their mindsets , way of life and perceptions have changed after accepting Islam this the Somalis became unified under one banner
except from one particular tribe that refused to embrace and remain reluctant to replace this foreign ideology with the religion of their forefathers, uprooted and pushed out of their wells, grazing lands and livestocks taken they were chased out from all corners until captivity and their women's taken as concubines some of the captives finally embraced meanwhile those who fled as far away to unfamiliar territories (Rendille,Samburu and Irqaw are said to be descendants of Meyle Samaale) meanwhile those who were captured and embraced Islam became outcasts or assimilated by the dominant tribes and history repeated itself
the powerful Arabs had pawns and influences they didn't need to conquest HOA when they had the full support of loyal Somali allies dying for their causes