Why are ebooks sometimes cheaper than paperbacks?

Whatthefluff
Like I get that cloud offers a chance to access an ebook through multiple devices. But physical labor and materials go into physical copies.
I have prime, right? So I see this book that's $10 for a print copy and $13 for am ebook. Because I have free shipping due to prime, that's likely built into the price of that $10 so that's no worry either.
Why are some of these ebooks more or equally as expensive as the physical copy? The only times I buy ebooks are when they are on that $5 or under deal! I'm not willing to spend more than a few bucks on a digital version.
Are they just hoping people don't notice?
Why are ebooks sometimes cheaper than paperbacks?
32 Opinion