Why? The program never said anything about it. Its a military workout, I don't think waiting between days is part of their program.
Everybody rests - even the military. In fact, in Marine Corps basic you only actually do PT 3 times a week. Granted the average daily routine is "PT" to the average person just by virtue of wearing/carrying 30 lbs of gear for 18 hours a day at a grueling pace but it's not PT. Rest is when you get growth, when you get recovery. You get nothing out of repetitive breakdown with no recovery.