My friend the Hyatt manager has repeated her brief insight. She is required to maintain a minimum level of walk-in inventory of suites and preferred rooms until well into the evening, lest the proverbial Courtesy Card holder or Hyatt Super VIP walk in unannounced and get stuck with a bad double next to the road. The one acceptable excuse when Hyatt calls to verbally throttle her is "we sold them all earlier".
If she has unbooked suites to spare they will first go to a frequent guest of her hotel, especially if on a one or two night stay. Late night random walk-in Diamond might hit the jackpot, especially if there is little else left.