There are no federal requirements for public schools to provide for Gym. State law varies considerably. Some states only require it up through elementary school, some up through HS but with reduced frequency, others require PE courses for graduation completion etc.
With our ever increasing sedentary lives some will argue that daily gym class is more important than ever. But with schools it's just one more non-academic offering to juggle into the schedule and budget.
Is physical education even education?
Should we 'teach' gym in schools?
Should the feds mandate minimum levels of PE offerings in public schools?