People have all sorts of "reasons" for turning against God -- rebellion against their parents' faith, a bad church experience, intellectual questions and doubts, and so forth. Often, I've found, they don't even know why they refuse to believe. They're like the Pharaoh in Moses' time, who "hardened his heart and would not listen" (Exodus 8:15).
What can you do? First, don't argue with your wife or try to get her to change her attitude; it probably would only make things worse. Instead, love her and pray for her -- constantly, fervently and trustingly. God is able to do what you can't do, piercing her defenses by His Spirit and opening her eyes to her need of Christ.
In addition, ask God to help you be a witness to your wife of Christ's love and truth by the way you live. She may scorn your beliefs and mock your faith, but she can't deny the life-changing power of the Gospel in your life. Jesus said, "By their fruit you will recognize them" (Matthew 7:20).
Finally, don't let her negative attitudes affect you. Instead, let them challenge you to an even greater love for Christ and His plan for your life. If you have children, do all you can to encourage them to put their faith in Christ and make Him the foundation of their lives. God's promise is for you: "To the faithful you show yourself faithful" (Psalm 18:25).