You're looking for rooms just as the major summer season kicks off (or just thereafter). Further, the tail end is just a few days before Independence Day. It's good to know the pace is picking up--if there's limited availability. What class of hotel were you looking for value, mod, or deluxe? Just curious which hotels are filling.
Also, travel agents do book blocks of rooms in certain hotels. . .that may be the case here, too.
Just a thought.