Oftentimes than not, couples that live together may not understand the many gifts that are received in marriage.
There is a diference between committing yourself in marriage and living together without an intention of making a commitment. Marriage offers a commitment by both to honor, protect, love and serve the union and each other. Both are making decisions that choose unity so the partnership will prosper. Each person brings to the partnership all that they are so both are celebrated for who they are. Contrary to what you see happening in marriages today, marriage is a spiritual commitment to love, honor, grow, protect and to serve your spouse for etenity in a loving spirit.
Those that choose the milk so-to-speak, do so because there isn't a commitment to provide an undivided focus on your partnership or your partner. They want all the benefits of a marriage and they don't want to get married. Living together without an intention for marriage says you really haven't committed yourself to loving this person for who he/she is right now. Living together without a future in mind with this person, you are basically still in the dating stage and at any moment you can choose to leave your partner. When you are in the dating stage it is easier to leave if the relationship is not working for you. In our society we like having options and leaving is easier to do than making an effort to work at loving another.