I presume that the publisher works on a wholesale price to deliver a profit on production costs and won't go below that until that level of profit is achieved. After that the wholesale price may reduce further.
The book sellers will go for whatever their corporate margin is on that product, and buyers love a cut price, so it's a win win win.
If it ever goes to reprint, production costs will be significantly less because all the design and formatting is done, unless I added an update chapter.
