While no single problem is exclusively to blame for the incredibly inflamed housing cost in Los Angeles, the generalized answer is that there are not enough houses to meet the demand, and in addition to that, the cost to build more housing keeps developers away. It is a vicious cycle of economics - people want housing, construction companies can't fill that demand because the cost to them is too high, this takes money and jobs out of the metropolitan area as builders, investors, and developers look to the suburbs to build, so the demand grows, and the cost grows alongside it.