When I'm shopping in an actual physical bookstore it often makes sense to buy a book that I won't be ready to read for a while.
First, if I become ready for it at a time when it is inconvenient to get to the bookstore to buy it I have to wait to start reading it, and that could be annoying.
Second, it might no longer be stocked when I get around to going back for it. I then have to order it, wait for delivery, possibly go pick it up if I order for delivery at the bookstore.
Third, I might forget about it.
With an e-book, none of these apply.
First, the e-bookstore is for all practical purposes open 24/7/365, and the book is only a couple of minutes away.
Second, it is unlikely to go out of stock.
Third, when browsing at an e-bookstore there is usually an easy way to mark books you want to get back to later.
Putting these all together, there is very little point in buying an e-book when I'm not ready to start reading it soon, unless it is on sale.
"The 45-chapter novel was published in 31 weekly installments in Dickens' new literary periodical titled All the Year Round. From April 1859 to November 1859"
Likely more people will read a book in short chunks because it looks less imposing. And it gives you an opportunity to "pivot" your story if it's not going well.
Most times if a book is expensive I'll put off buying it, but if its a dollar or two, no love lost if I only read a few chapters and don't like it.
B) When I was homeschooling my sons I frequently bought actual (dead tree) books for a dollar or so off the clearance tables. It was cheap enough that I was willing to gamble on their usefulness. Some panned out. Some didn't. Enough panned out for me to feel it was still well worth it.
I've always wondered how much more money Amazon would make if they didn't highlight unread books, and how much people would care about the lack of that feature.