Two reasons why:
1) Arrogance
2) The word 'Teamwork', is an alien concept.
Somalis think they are good at football, just becuase they are able to pass multiple opposition players and score a banger, when playing at the local council cages or the school playground. Then this sense of arrogance, that they are the best from all that time in the cages or in the playground: shatters once they join a pro or semi pro team. The reality of how mediocre they seeps in, then theres no desire to better themselves, give it their all in training. Basically, laziness is what destroys their footballing dreams.
There's this greedy nature with Somalis, when playing the game. They hardly pass, how many times do I hear team players screaming their lungs out to the Somali's name: "Abdi, Abdi, pass the ball!!" "Ahmed, over here!, lay it to me!!"
They think they're Peel, doing single runs every single time they touch the ball. This is something I've seen in every single decent Somali kid. They do about a thousand step-overs in every damned game. The word, teamwork, does not exist to Somalis playing the game.
These two reasons, I think is why Somalis hardly ever go pro. Arrogance and greedyness, is what prevents great young Somali boys from becoming footballers, it's very simple.