Three reasons. (1) Like others have said, it sets a dangerous precedent for the world to recognize states that form during continued widespread political instability in a country. For obvious reasons. (2) Contrary to one assumption found in other answers, Somaliland is not unanimous in its desire to be independent, there are in fact several tribes and regions within Somaliland’s unofficial borders that consider themselves unaffiliated with the concept of a Somaliland state, even if they don’t accept a united Somalia state concept either. (3) There has been significant investment, as mentioned, in the formation of a Somali state based in Mogadishu, and through the investment process attempts are being made as we speak to ensure that various groups have their strategic interests met prior the consideration of any strategic interests Somalia has. I recommend you look up how much money in international aid has been sunk into Somalia, in the form of military aid to Amisom countries and humanitarian aid intended for Somalia or Somali refugee camps in northern Kenya. The aid stalls and is wasted (one way or other) in Nairobi Kenya, never to reach its intended recipient in desperate need. That’s a long way of saying other countries and even development agencies don’t give a crap about a stable Somalia so even if Somaliland offered great vastly beneficial opportunity, it’d be ignored because it would slow down the aid flows and military financing upon which thousands in the region and a few governments are now dependent upon for survival.