The mitzva of Torah study includes two elements. The first is to know the Torah’s teachings on faith, halakha, and morality. This knowledge is a prerequisite to living a Torah life, so all Jews are obligated by it, both men and women. The second element is to go further and study Torah in greater breadth and depth. Men are obligated in this type of study; women who wish to engage in it are performing a mitzva, but are not obligated to do so. The more free time a woman has, the more it behooves her to undertake this advanced Torah study as well.
For much of history, life was simpler and was lived locally, so practical halakha could be absorbed at home and only a minimal amount of formal study was necessary. Children would acquire the foundations of faith and morality through conversations with their parents and older family members. More recently, the world has become more complex, and all fields of study have expanded. The first element of Torah study has greatly expanded as well. Therefore, the difference between men’s and women’s obligations in Torah study today has narrowed significantly. In fact, many men and women do not manage to master the areas where everyone has the same requirement.