i am totally agree with you, secondary students have more lessons and more subjects. So, if every week have more 2or 3 lessons to take PE. We would have more time to relax ourselves. And the age of 13to 17, it is the important to grow maturity of our body. So exercising is more important.
And other good reason, after we take PE lesson, we will have a fresh spirit to take the other course. It like to recharge ourselves.
Moreover, our school still only have 2 lessons a week, the schools said our learning is busy. So, they encourage ours to do exercise when lunch time extra-curricular activities