[medprof]

Because sex is a sensual pleasure for the most part which can cause disturbance of the mind and even addiction. It can also create social obligations such as parenthood, which a monk cannot spare time for. This is not the only sensual pleasure monks do not engage in. They avoid high seats, many meals a day, extra clothes, possession of money or property etc. Less baggage to carry around. Monks and nuns adjust their lives to directly support the practice. Celibacy is part of it.