Perhaps, because it is a wonderful and celebrated function of the human body, to be enjoyed within the confines of marriage - as designed by our creator.
Looking at scripture, I see no prohibition - or even discouragement - of the practice. Are you aware of any?
We live in a Josephite marriage but would not be permitted to have sex by our church anyway, if we are to continue receiving the Holy Eucharist.
It should be a requirement of marriage that every couple read together 1 Corinthians 7 every day…. 1. Now concerning the things whereof ye wrote unto me: It is good for a man not to touch a woman. 2. Nevertheless, to avoid fornication, let every man have his own wife, and let every woman have her own husband. 3. Let the husband render unto the wife due benevolence: and likewise also the wife unto the husband. 4. The wife hath not power of her own body, but the husband: and likewise also the husband hath not power of his own body, but the wife. 5. Defraud ye not one the other, except it be with consent for a time, that ye may give yourselves to fasting and prayer; and come together again, that Satan tempt you not for your incontinency.
Far from discouragement, it is essentially mandated that a married couple have sex… it’s called ‘fraud’ if one party in the marriage denies sex to the other and in fact the principle of marriage as laid out in these brief verses is that each person place the complete power over his/her body to the other. If either party want sex, the other party has to accommodate the need. How’s that for trust? And the only acceptable reason for holding off on having sex is that the couple mutually agree to do so for the purpose of prayer.