This happens to me, too! If I read a physical book I can easily recall the author and the title months and even years later. But when I read digital books I often struggle to remember a book’s name and have to look it up if I want to recommend it to someone.
My guess is it's mostly because the physical book's cover's always visible in your environment, even when you're not reading, so you see the title and author's name a lot more. Some e-readers put the cover on when in sleep mode, but that's small, black-n-white, only on one side (no spine) so it's easily covered up, et c.
Books also often put some or all of that info at the top of every page or every other page, while many reader apps hide it most of the time, I suppose to save space for body text.
OneAd free Kindles (can) display the cover of the book you're currently reading during idle mode. I love it because I used to leave a book on a coffee table or my desk as a kind of physical invitation to read (instead of watching TV or playing video games or derping on my phone).
Such a tiny feature, but since I've turned it on it has nudged me to read hours more each week.
