I had a discussion with a Cluster General Manager about 3 years ago. Wanted to extend my stay by 1 night and asked at the front desk. Was denied, because no availability.
Via Website many rooms and room types available.
CGM explained, that there’s less relation between Hilton Website and actual inventory.
And yes, I should have booked instead of asking. But at that time, I had ~100 nights at that property and didn’t want to cause issues.