It is not as old as time. It is a very new phenomenon where both sexes now work towards equal earning power, seek absolute freedom without dependencies while child care is professionally commoditized. At the same time, entertainment is not only plentiful and cheap but typically of higher quality than any marriage can provide beyond honeymoon period. Add on the top of this very extreme cost of divorces (in state of CA it translates to lifetime slavery) and most young people very acutely aware about this as half of themselves comes from divorced families. They innately understand this "love" thing is transient, expensive and very time consuming.