Because marriage is not the end goal of our existence, God uses it as a tool to prepare us for glory. It's one of the many things in life that he will use to grow us. He can use marriage to teach us how to cook, to make us more gracious, to develop our communications skills, etc. Perfection isn't required for marriage, getting your self together isn't a requirement. I think you can have it all wrong and God can and will use your marriage to grow you up in Christ. Because the pinnacle of life is not marriage, it's Jesus and to become more like Him.
I knew a girl that was very insecure, didn't say more than two words. Needless to say she was a bad communicator and really struggled to connect her emotions with her words. She didn't enjoy God's Word and didn't understand the gospel. She believed she was saved by grace through works and was often discouraged by her failures. This girl met a wonderful guy who pursued her despite many voices telling him to stay away. "She's not prepared," they'd say. But God graciously kept him pursuing her. I should say this guy wasn't perfect. He had a thing or two to learn about communication. He struggled with being too good at connecting his emotions with his words and could be a bit harsh. But He loved Jesus and shared the gospel often in their dating relationship. A little over a year later they were married and a year after they'd been married, the Lord opened the girl's eyes to the beauty of the gospel. She finally understood she didn't have to work for her salvation. Jesus did it all for her. Then the following year they found out they were expecting. They were excited and nervous but trusting God would work out the details. 7 months later, they're son passed away at 31 weeks. God gave that girl grace to find joy in suffering. He gave her peace that surpassed understanding. He showed her he could use her for his glory. He showed her she had value and worth and was put here for a purpose and gave her a voice. Her son's death gave her life. And that girl was me.
I was the one person that you would say was unprepared for marriage, but somehow God saw it fit to take me from singleness to marriage and graciously used my marriage to teach me how to do things I struggled with being single. I share that story because I hope it encourages someone to see that God uses all the "life changing" events like marriage and children as a means to grow us, not as the things that we should be 100% ready for. Because honestly, He will make sure there will be challenges that we are not ready for, so that we fall to our knees and depend on him. I just want to encourage my single friends that the reason why you're not married isn't because you aren't prepared enough, it's because God is growing you up to be more like him in your singleness. His goal is Christ-likeness not marriage. There is nothing wrong with you, (well there is, but that's taken care of) you are not forgotten, you are right where you are supposed to be. No need to wait around for life to start. Life has started, you're in the middle of it, God is working in you now. Live.