Quite simply because exercise is the most ineeficient way to lose weight and burn fat.
The bok relies on 3 principles for weightloss:
1) Diet getting you into a deficit
2) Depending on which book the weights routine may provide all the cardio benefit you need, if its combination exercises of supersets, tris and quads, minimal rests and working to exhaustion with a slow cadence for example
3) Th etype of running routine you are talking about is called HIIT, High Intensity Interval Training and EPOC, (basicaly the alleged afterburn) HIIT gives you more bang for your buck than normal long distance runs when your body conserves energy to last the endurance aspect. HIIT also elevates the heart rate which then means after you finish you will continue to burn more energy. Combine that with the weights and retained muscle then its the perfect recipe for giving the metabolism a kick up the arse.
I personaly wouldnt rely on training at all to burn an exact number of calories, its too erratic and far easiet not to eat unneceary calories in teh first place ie it takes seconds not to eat 500 cals yet 40 mins average CV to do the same.
the reason the book says dont deviate is quite simple. Energy provision is calculated so that you have sufficient for the training and still to create a deficit in calories. If you add more exercise or training you will crete too greater a deficit and your fatloss and indeed metabolism will eventualy start to slow down. You will still continue to lose weight but at a slower rate than you could have.
At the end of the day I look at it like this, people often raise the questions as to should I add more or I feel I am not doing enough. But on the same basis they didnt have the knowledge to stop themselves getting overweight in the first place, (dont get me wrong I was the same and was a fat sod for years until I started reading up). So why spend your money on advice and then think you know better? It doesnt make sense when you look at it like that does it. But sometimes less is more, not something you hear said often in gay society PMSL
You will probably find it takes a good 3 weeks to really hit the sessions correctly and then you will be saying "shit I couldnt do any more if I tried". So stick at it.
As for the initial phases of the book its conditioning for an untrained body its the initial stages. You will make muscle gains as you begin but in a deficit calorie situation this will not continue, strength will though.
I personaly dont do any running and still lose 2 lbs average a week and have a far greater CV ability than ever befor. But thats down to the structure of my routine.
Good luck with your training