The primary purpose for the "recommendation" of marriage before ordination is so that the pastor has a mate by his side to support him in ministry to the churches he serves. Second, marriage also commits the pastor and his wife to making sure they protect and help each other in times where questionable situations may arise. One can most certainly argue that being married presents a less likelihood that he (the pastor) would fall into questionable conduct. Marriage does have its "safety net" as is reference in Ellen White's writings about Adam & Eve. She clearly states that Eve fell into Satan's trap because she "left the side/safety of her husband".
Pastors have a great deal of responsibility when it comes to the challenges of ministry. There is room, I believe, for every unmarried pastor to examine his limitations when it comes to the women of the church. I am an unmarried pastor and would try my best never to be caught with a female in my office alone, with the doors closed. Or, having "private" counseling, bible studies, home visits, etc, without the accompaniment of a "trusted" older mother/Deaconess/Elder by my side. If I am unable to obtain such support as that, then I am limited in my exposure to you as a single women having me in your home or in private spaces. Single pastors need to lean heavily on the "protection" and "safety" of the church.
Last, the single pastor must by any means necessary, protect his name and reputation. He sets the boundaries of how his "single" status will limit his conduct. He must ensure that no reproach is brought upon himself, the church, or the conference he is employed by. Though a time may arise where the single pastor is now courting/dating. He must still, even then, ensure his conduct is above reproach in the places he and she go, the conversations, etc.