It was used for centuries as the written language of Somalis. Sometimes, like with Far Wadaad, people wrote Somali or a mix of Somali and Arabic using the Arabic script but a lot of the time Arabic was straight up the language of commerce, record keeping and communication. Most historical manuscripts, elite written letters of correspondence and so on we have from the last 300-400 years are in Arabic but written by Somalis. Most of the politicians of the Somali Youth League could speak Arabic and write in Arabic and frequently read Arab newspapers. It was sort of the medieval Latin in Western Europe of our culture. Very much a second language if you were a merchant, judge, ruler or any sort of traveled and learned man. Somalis are also a deeply religious and proudly so lot and given Arabic's inseparable connection to Islam that only helped seal why our founders would want to enshrine the language.