As Chip B wrote, the rest day was called for one reason only.
Safety
9 Straight days of racing under any conditions increases the potential for accidents by pilots, tow pilots, and ground staff.
Adding to the risk is the heat, age...both young and old, and experience of some.
The blue day was mentioned only as an indicator as being the worst of the next 6 days. Plus, while not a rule, Nationals have always had a rest day since I have been racing and that makes it standard practice, from a litigious angle.
Finally, you put the hosting organization and staff in an unacceptable risk position.
The contest staff are very good, very smart, and very wise.
R