Work experience is important to business schools because they want to be sure that accepted applicants can contribute to the program. Business school is a give and take experience. You are able to obtain (or take) valuable knowledge and experience in the program, but you also provide (give) unique perspectives and experience to other students through participation in discussions, case analyses, and experiential learning.
Work experience sometimes goes hand-in-hand with leadership experience or potential, which is also important to many business schools, particularly top business schools that take pride in churning out future leaders in entrepreneurship and global business.