I usually book my hotel in Hua Hin early June but it looks likes today my regular Grand and Plaza Hotel does not allow it while it's mid July already...
Due to present market conditions and predictions for the coming high season many hotels do not know what to do.
A typical Thai marketing strategy is let's see what the competitors do first.
Also many hotels delay the issue of new rates pending the outcome of negotiations with new investors, potential new owners and the big western travel operators.
Ask your travel agent for a quotation. Possibly cheaper than booking directly with the hotel. Upon request they will issue rates to an official agent or at least inform them why they cannot.
We are all living in 'the good old days' of the future.