It’s because the word ‘Somalian’ doesn’t exist. It’s made up by some ignorants who couldn’t care less about Somalis and now even some of us are using it. Saying ‘Somalian’ is basically as nonsense as saying ‘Pakistanian’, ‘Bengalian’, ‘Moroccanian’ etc….Stupid,right? I hope you get the idea.
'Somali' is the correct term. Use it & correct others :)