It's a weekend, the Not so Scary Halloween party is going on, it's about the time most schools have fall break, and it's a time a lot of "snow birds" start hitting Florida.
It's very possible they really don't have a space. I'd just keep checking. Talk to a real person and ask if it's because you only want one night, but I doubt it. That doesn't sound right. They don't care who uses a room or spot for how long, they're going to fill them regardless.