Parmandur
Book-Friend, he/him
There is also no warehousing that needs to be cleared for digital products.Kinda guessing here (I'm not in the industry), but I think one of the other factors in the OP's complaint is competition. We're used to older books having lower pricing than new books, partially because physical retailers know that used books are an alternative option.
But I think some digital publishers have essentially decided/speculated that their key market for people who buy digital books won't consider used books as an equivalent option. Their key demographic wants that old book in digital form, and will pay new book prices for it if required.
And if you raise the price, you can juice sales by introducing deals once and a while...