Because they want to reject respect for the flag and anthem instead of the police chiefs and mayors that fail to enforce police discipline. Police, of course, should not be allowed to form a "gang" to control local government, ie. POLICE UNIONS. The DOJ has poked into these problems over the decades, but failed to make the basic changes necessary.
The KEY: "unions" are sacrosanct in the minds of far too many people. At the very least, police unions must be prevented from nullifying police discipline to elected officials. The problem isn't "the nation and its symbols" except for the extreme left going for overthrow under the pretext of police reform.