1. A single woman has more time to devote to church functions. With no man at home to tend to, she can stay all night cooking, cleaning, and doing work at the church instead of spending time with a husband.
2. A single woman has the clergy guilting her into paying more in tithes and offering, whereas if she was in a relationship, she would have to confer with her mate on finances. If she has a man, maybe he's telling her to pay less to the church and save to pay bills, go in vacation, buy things for the household.
3. This is the most important. If she doesn't have a man in her life, God/the pastor is the man in her life. She fuels all of her energy and desires into church. Introduce a man, and now her attention is split and she's not as worried about what the congregation has to say about how she lives her life. Next thing you know, they have one less church member.