The biggest single reason for divorce is the present day aversion to COMMITMENT! Most are afraid of it and a large number really don't understand it. It sorta like "I'll try it (marriage) for a while and see if it works out. zero commitment. Something will make it NOT work out.
There are predominating sociocultural factors which engender an antipathy toward the maintenance of marital commitment.
One such factor is the concrete expectation of custody-advantage in divorce.