They don't explain it at the desk but the BG rates are for 30 minutes while the SG are only renting the rooms for half the amount of time (15 minutes). That is why their prices are usually half as much, too. But with the HK hotel the ratio is now less since they raised the rates for 30 minutes but not for 15 minutes.
HK is spending a lot (capital improvements, edecanes, advertising, promotions, special events) and they are making it back with the hotel fee increase, nonsense like the $1 robe fee, super aggressive maseros, wandering salespeople (flowers, gum, photos), etc.