I'm not a successful author, but I always publish a print book at the same time as the eBook.
Here is why I do this:
1, I have already paid for editing the MS as an eBook and therefore a print book requires no further editing input.
2, I use the free ISBN and it costs nothing to upload.
3, I already have the eBook cover, so there is little additional cost to add the spine and back cover.
4, I format my own, but even using a formatter costs little.
5, The print book on my sales page shows a considerable saving over the cost of my eBook, but it also allows me to show a price of at least $3.99 for the eBook without it looking too stupid a low price. In other words it gives the notion the eBook is value for money at a reasonable price point.
6, The vanity in me likes to show something tangible for my efforts by way of a line up on my bookshelf. It also proves I am an author to those who visit and take an interest.
7, I know it s virtually impossible for self-published to get distribution to bookstore shelves,so that part doesn't bother me.
8, As someone said, proofing a physical book can help to discover errors.
As I have said, I am not a successful author and yet I can't understand why anyone who is successful, or not, would leave both money on the table, or not use a print book as part of their marketing budget to show the discounted price of the eBook.
By definition, a successful author will have visibility. Without a doubt, people buy print books from Amazon.
I sell 5/10 print books per month of the first book in my signature, courtesy of visibility via sponsored ads, so you don't need to be successful to sell a few print books to cover costs. That book doesn't sell enough eBooks to give it what I would call a successful cat rank, but it has visibility via the ad. This gives me a small annual income of around $400 for the print version + some print sales on my other books, and so that more than covers the cost to have having my next print book available.
In the interest of transparency, I format print books for clients, but what I list are genuine reasons for me to publish my print books.