Say you book 4 nights in June at a particular rate. You are making an agreement with the hotel that you’ll be there for 4 nights and the hotel agrees to take $XX per night.

in September, you decide maybe you don’t need that 4th night and now you are essentially breaking your agreement with the hotel to occupy that room for 4 nights. But in the meantime rates have been going up for 3 months. And now the hotel has to sell an additional night to someone because you’re leaving a day early.

So you aren’t holding up your end, but you expect them to offer you the same rate? Doesn’t work like that. If you want 3 nights today, your reservation gets repriced at today’s rates.