There appears to be enough evidence of a decline in interest in physical education among girls for a closer look at the issue. Studies are showing that only some 20% of girls elect to continue physical education classes after the mandatory course-work is completed.
As explained in the linked article here, the reasons are not difficult to understand. One thing left out of the article are members of either sex who do not fit the norm; that is, competitive girls, and cooperation-minded boys. We know that such individuals exist.
Overall, however, the article tries to be fair to both girls and boys. A worthy goal:
Promoting Girls' High School Physical Education