Because, a religous education director is generally NOT a nun. There are some nuns who are religous education directors, but not all of them are. There is no requirement that a person has to be a consecrated religous, (nun, preist, or Brother), in fact there are many lay people who take jobs in the Church, such as youth ministers, or religous education directors. If the RED is married, then they are not a member of the consecrated religious. Nuns, preists, and Brothers take a vow of celibacy, but that is not required of all who work in the Chrurch. As I have said, there are also many lay positions. There are also deacons in the Catholic Church. A deacon is different from the preist, they are meant to help the preist, and are generally already married men. A man must marry before he becomes a deacon; he will not be allowed to marry after he becomes a deacon, nor can he remarry if his wife passes away. A deacon, obviously, makes now vow of celibacy to God, unless he isn't married. In any case, to answer your question once again, the DRE can get married if they are not a celibate preist or nun, if you know a DRE who is getting married, then they are not a preist or nun, and, not all people who work in the Catholic Church are preists or nuns, or Brothers.
There's your Catechism for the day.