Religious reasons: In many cultures, women were not allowed to perform on stage. This was because it was considered to be immodest or inappropriate for women to appear in public. In some cases, it was even forbidden by law.
Practical reasons: In Shakespeare's time, there were no professional actresses. All of the acting roles were played by men. This was simply because there weren't many women who were trained as actors.
Artistic reasons: Some actors believed that men were better suited to playing women's roles. They felt that men could bring more depth and complexity to these roles than women could.
Over time, the practice of men playing women's roles gradually declined. This was due in part to the growing number of professional actresses, as well as changing social attitudes about women's roles. Today, it is rare for men to play women's roles in plays.