They can't relax unless everything is perfect. No wonder tremendous pressure interferes with every aspect of life. Enjoying sex just becomes too complicated. Together, talk about these possibilities. But it isn't true for all women.
Men tend to feel more open, relationally, to their wives after sex.
Women tend to feel more sexually open when there is relationship intimacy. Being emotionally vulnerable yourself might make a huge difference to her. Since men and women come at intimacy from different directions, you might be wise to take a look at how she sees the problem. Louis mentioned the issue of power or control in your relationship. If she does, she may be withholding sexual intimacy because it's the only area of your relationship where she can feel that she is in charge.