I've seen points only rates there before.
I think it's has to do with inventory. Hotels are required to make a certain amount (not all) of base rooms available for points. Points plus cash is usually a bad deal for you... And in contrast, a better deal for them. So I have a feeling that hotels like this one, allow for the lowest possible amount of rooms to be booked fully on points, and then make a few more available as points plus cash.