It sounds like the OP checked online rather than calling Reservations. It's possible he got caught up in something as simple as a limit to number of rooms that can be booked online (irrespective of room types). Airlines have the same kind of limit. Booking more than XX (and sometimes that is fewer than 10) demands a call.

It's also possible the hotel is 'fully booked,' having sold some inventory to 3rd parties, and now the hotel sales agent is going to try to claw back some rooms for direct sale. Pre-selling to 3rd parties happens every day, and rooms get resold through both opaque (Priceline Express Deals, as an example) and transparent channels.

Instead of researching this, some people are quick to spin out and call this a bad business practice or something nefarious.