There was a very deliberate reason behind why they inflicted economic devastation on Somalis and did everything possible to prevent Somali advancement.
First, as you pointed out, Somalis were a self-sufficient and commercially organized society. Colonial powers sought to crush this independence by dismantling Somali industries and blocking local economic growth, deliberately creating dependency.
Second, Somalia was experiencing a major economic revival in the 1800s, driven by domestic trade, industry, and expanding commercial networks. The colonial aim was to destroy this momentum to weaken resistance.
Many Somali merchants were forced to move abroad to establish their companies and factories, because at home, they were blocked from ownership, licensing, and industrial growth.
It wasn't just the economy they targeted , they dismantled Somaliaās educational system as well. Literacy in the Arabic script was widespread before colonization. Somali intellectuals had established vibrant madrassas, book publishing centers, and trade routes that spread scholarship and Islamic learning.
The British seized Somali publications, restricted book imports, and broke the networks between Somali scholars and the wider Islamic world. This systematically alienated Somalis from both Somali and Arabic learning traditions.
When you look at the Kacaan government's famous literacy campaign in the 1970s, what they recreated was not new it was a revival of what Somalis were already doing in the pre-colonial period: learned students and sheikhs traveling across the countryside, camp to camp, village to village, town to town, teaching Quranic studies, literacy, and spreading education.
Colonialism did not just 'fail' Somalia ,it actively sabotaged a self-sufficient, literate, economically organized society to impose dependency.