It makes no sense, and I've asked this question probably a half dozen times with no compelling answer from anyone.
Assuming occupancy of below 90-95%, the hotel doesn’t lose anything by offering rooms as their costs and then some are covered by the loyalty program. Now, assuming occupancy above 90-95%, the hotel gets reimbursed at the ADR or some such other metric, so there they also lose nothing. In fact, they gain considerably.
So what’s the motivation to play these games? Fill up enough of your hotel with awards and all of the sudden each booking is reimbursed at ADR! And even if you don’t succeed, it’s not like the hotel loses.
Put otherwise, if the hotel is operating at or near capacity, it gets reimbursed the average daily rate or some similar amount. So, in that case, they have no incentive to not offer rooms for awards.
If the hotel is NOT operating at or near capacity, they have excess rooms that will simply go vacant for the night. In that case, what’s the incentive not to offer award rooms? The variable costs?
Further, if the hotel is operating at say 60% capacity, and they release the remaining 40% inventory for awards, it’s very likely, given how popular this hotel is, that the rooms will fill up, taking the hotel passed the magical line between “basically no money” and “ADR” for all awards. (Unless it’s only ADR for those awards booked past that magical line, but even then…)