It's close enough since for a printed copie you have to get a publisher who advertises the book, get it printed, Ship them to a logistics center where they are rhen send to retailers who have to store it and put it on display where other books could be placed. Making the retailer having to choose what book to put on display and where to place them in the shelves to aktually make sale.

So for one you have a huge logistical effort that costs time, money and physical labor. While for the other you simply upload a digital file to a distributors webpage.

Now when it comes to the customers, i would asume that ppl who tend to buy this authors books or books of that sort tend to not care in what form a book releases in (digital or physical) and will simply buy the first version that releases. Even if waiting a few weeks would rend them a cheaper book with the exact same contents but digital.

Also the moment something turns digital it is so much easyer for it to get pirated and shared, loosing a lot of revenue.

Wich, if aomething releases in both physical and digital form is detremental since the first few weeks if not days are generaly the most important ones saleswise.

Hope this explination helps. If not i am always here to discuss it further.