Actually they did write, but most of it was records of genealogyIt's truly sad that somalis don't write their own history but alhamdulillah other people wrote
about the somalis instead so we have something to go on from. If you're looking for a historical source here is something right around the time of walashama establishing their kingdom at the tail end of the 13th century an arab writer by the name of Shams al-Din
al-Ansari al-Dimashqi wrote the following
جبل خافونى بأرض الهاوية وسميت الهاوية تشبيها بجهنم في حرها ونارها ثم بأرض بربرا وبعض بلاد دمدم
( والحبش السفلى ثم بأرض جبرة ثم بأرض باضع ( ثم بساحل زنجبار وأرض الزيلع ثم بأرض أوتل
meaning
mountain of hafun in the land of hawiya and it's called hawiya because it's like jahanam in it's heat and fire (hawiya is one of the names of jahanam) then at the land of berbera and some of the land of damdam and then lower habasha then the land of jabart then badhe' and then the coast of zanzibar and the land of zeila and the land of awdal.
In this text it's writen أرض أوتل meaning the land of awdal.
How do modern day arab understand this. Here is a text from the 90s explaining it.
وأرض أوتل . ويقصـد بـأرض جبرة بلاد مملكة أوفات ، كما أن اسـم " أوتـل " تحريف اسم عدل أو أودل الصومالي
meaning
and the land of awdal, and they mean when they say land of jabart the land of the kingdom of awfat, and the name adal is corrupted form of awdal Al-Somaliya.
Al-Dimashqi is also the first to write xamar.
مقدشو الحمراء
meaning
the red mogadishu or mogadishu al hamra'