Which part of the Bleach universe exactly made you think it's fair at all? When normal people die, their souls proceed to that wretched medieval city in the SS. The few lucky ones with some reiatsu may gain access to shinigami bastion itself (whatever was its name) and perhaps get a better life (assuming they like somewhat strict and dangerous military life). If you decide not to go there despite having reiatsu, you become an outcast hungering for the ever scarce food.