Cohabitation is just a way to avoid the full commitment of marriage. Should it fail, I owe you nothing - you go your way and I go mine. This is very common in places where marriage laws favour a particular gender more. The gender that's affected most by such laws, may opt for cohabitation as a means of safe guarding itself from such skewed marriage laws.
Cohabitation could also be as a result of unpreparedness for the responsibilities and challenges of marriage. Have you noticed that a cohabitation relationship breaks faster when there's a problem than a marriage relationship? Most people don't want to fulfill the responsibilities of marriage that's why they opt for cohabitation. The truth is that, should it fail, one partner is always at the losing end and the partner at such end most times is the .......... Fill in the blank space. You're the that filled it o! Lol