Physical Education and Academics

According to a recent report, physical education is so important that it should be a "core academic subject." (see here)  So, why is it that Illinois schools are constantly trying to get waivers from the state to remove physical education from the school day?

This idea that physical education is closely tied to intellectual education is nothing new.  The Latin phrase "mens sana in corpore sano" ("a sound mind in a sound body") expressed the same idea.  The ancient Romans were well acquainted with this idea.  Why do we insist on having to relearn things that have been known for centuries?