Of course not, since the guaranteed availability rate is essentially an "oversell" rate which could likely lead to another guest being walked.

However under normal circumstances when rooms are available, I do not see why the daily rate would be unavailable. I suspect this might be a stratagem to circumvent the "no capacity controls" policy that allows any available standard room to be booked as an award, and/or to avoid honoring the "My Elite Rate" benefit.

Other hotels have done things like this, IIRC. PH Vendome once did not offer standard rooms for single night stays, even though the nights were available if booked as part of a multi-night stay. This may have been an attempt at controlling award inventory, since award rooms would not show as available if nights were searched for individually.