Its because no self-respecting country has a state that believes they're a seperate entity.
After the Rwandan genocide, Paul Kagame pleaded with the Tutsis not to secede and they heeded. Due to that, they reached better than they would have separate.
Somalia's biggest problem today is Al-Shabaab and we should focus on that. But one must realise that Somaliland creates a dangerous precedent in Somalia. After all, nearly every state in Somalia is divided amongst tribal lines and if SL secedes it creates legal precedence for PL to secede as they were once a sovereign kingdom.
TLDR: Somaliland benefitted more economically and politically from uniting with Somalia but wants to leave when Barre, who targetted everyone, targetted them.
NB: If Somaliland achieves independence, I will be happy for them but SL and Somalia share the same religion, language, culture and ethnicity. The only reason for separation is qaabil.