Here is how that works, presented in diagrams.
1) There are more women than men in church, of varied levels of spiritual understanding. It is humanly impossible to accurately measure spirituality, but for the sake of this point, I will call a level of understanding that only get “Give your life to Jesus, he saves” and acted on that, a 4. (A level of spiritual understanding that do not get that part is not Christianity.) 10 represented a spiritual understanding as deep as is possible on this earth. The levels of understanding will not be distributed as evenly as below, but I draw them that way for the sake of simplicity.
Blue represent church men, and pink church women:
2) A spiritual leader cannot lead anyone ahead of him, so any given man has to marry only a woman that is less spiritual than him. The man marked as 4, the newly converted man, is unmarriable. For one thing, a Christian should not marry a non-Christian. For another, he cannot marry a woman he cannot lead spiritually. And the woman should let the man lead spiritually, so the woman marked with a 10 is unmarriable too – It is not the will of God for her to marry a non-Christian or anyone who cannot lead her spiritually. God want women to be spiritually led in marriages, if complementarians are right.
Here, there are lines from every man and woman to the partners they may possibly marry:
3) Assuming none of the men have the gift of celibacy, and all want to marry, we can, for example, pair Mr. 10 with Miss 8 and Mr. 7 with Miss 6. It will mean Miss 10, Miss 4 and Mr 4 is unmarried. Mr. 4 can get married if he grows spiritually, Miss 4 can only hope and pray that God will rise up some mature Christian man, and Miss 10 cannot even hope. In this diagram, each man has his marriage partner and the singles are marked with red:
It is obvious that the complementarian church will have some single women, and more of them according to how much they actually believe (as opposed to paying lip service to) the spiritual leadership doctrine.
But the so-called female roles in complementarianism relate to husbands, children and the home. Paul said it is good to remain single, for “the unmarried woman careth for the things of the Lord, that she may be holy both in body and in spirit: but she that is married careth for the things of the world, how she may please her husband.” A complementarianism that say the things of man – him, his home, his children – is the spiritual purpose of women is the diametrical opposite of Paul in Corinthians.
A church that cannot answer what the single woman’s special role(s) is(are), cannot call men and women “equal, but different.” It has, unlike Paul in Corinthians, no real place for a lot of the women in the church. Is it any wonder that the percentage of women in church is falling faster than the percentage of men?