There are several reasons for this, but the biggest to me is a philosophical reason to Pavel's way of lifting. It's "practice" rather than "training".
When you want to be good at something it must be practiced most days. If your practice begins to suffer then it's time for a break. If you aren't still feeling fresh after a practice session then you over did it in some way. Possibly too heavy a weight, too much volume, not enough rest between sets.
The Russians and the Bulgarians both used this technique for Olympic lifting. Training both the C&P and the snatch briefly each day. Sometimes a couple of times per day.
Don't confuse S&S with a bodybuilding program or any other program that promotes hypertrophy. For this rest and extra calories are king once the muscle is stimulated.
For some 6 days per week may be too much just due to lifestyle, stressors, age, or genetics. Everyone's different and you must find what works best for you.
The other thing is that S&S is suppose to be a program that you can do to improve other aspects with the minimal amount of time invested. A program that allows you to train for strength improvement while still allowing you time for practicing your chosen sport, job, or just life in general.