I took the points for this promo, but Hyatt award availability is usually pretty good so I think at least some of these issues must be from people trying to book these incorrectly and by incorrectly I mean assuming that Hyatt's online booking tool actually works.
The comments about the various issues with booking these online are spot on. You can usually only book one night at a time and even then you'll sometimes get errors that you shouldn't. I almost always start with checking revenue bookings for a property's standard room and then call if it won't let me book online.