Ultimately, Ringo, the question comes down to God's authority over His creation. After all, it was He who created mankind in two genders, male and female. Additionally, it was God who determined the roles men and women should fill. While equal in value, men and women are not equal in function. Speaking broadly, God designed men to lead and women to follow. But this doesn't answer your question...why?
Ephesians 5:21-33 is perhaps one of the best known passages dealing with the relationship of husband and wife. It begins with the admonition to all Christians that we should be subject one to another. The Apostle Paul, who wrote the letter to the Ephesians under the direction of God's Holy Spirit, then goes on to provide three examples that characterize this submission.
1. Husbands and wives
2. Parents and children
3. Masters and slaves
While many in the feminist community like to use verse 21 --- "Be subject to one another in the fear of Christ" --- as justification for mutual submission where no one leads, this is to ignore the context of the passage. Take a look at the three example relationships, only start with #3 just to clarify things a bit. The slave is commanded to obey and serve his master with all diligence, while similarly the master is called to treat his slave fairly, since God doesn't play favorites based on human social distinctions. Nevertheless, the master leads and the slave follows; never the other way around. Similarly with parents and their children; the parents lead and the children obey. These are example of human relationships that manifest the truth of verse 21 --- submitting one to another.
Then look at husbands and wives. 5:22-24 makes it clear how a wife should submit to her husband. "Wives, be subject to your own husbands, as to the Lord." [5:22/NASB] Notice the relationship between a woman's relationship to her husband, and her relationship to Christ.
Likewise, in verses 25 and following, we see that husbands are to love their wives just as Christ loved the church and gave Himself up for her. When believing men and women are living out the kind of marriage God prescribes in His Word, they are saying something very important about the relationship between Christ and His bride, the church. In fact, 5:32 makes it clear that this is the very thing Paul was getting at to begin with. God engineered marriage to reflect the union of His Son to Christians.
So here's the big "WHY": Why is biblical marriage about the husband lovingly leading, and the wife humbly submitting? Because in the eternal relationship between Christ and the church, Christ leads and the church submits --- NEVER the other way around.
But I have an even bigger question for you --- one you're going to have to contend with if you're ever going to resolve this issue. There is no question as to what the Bible teaches about marriage. The only relevant question for you is ... will you submit to God's authority over your life?