I'm missing this too. One reason that publishers sometimes keep books in print despite near-zero sales is that they think the writer is good enough to score a major hit someday. If that happens, all his/her previous books are back in play, sometimes in a very big way. If the publisher is willing to take this risk, it should have the right to keep these in print.
And as is also clear from the above, the only time an author's sales are genuinely gone is if he/she never writes a successful novel in future.
You're missing this part -- if the author is now successful, he/she is in a stronger bargaining position. Which means, had the rights to the original works reverted back to her, she could sell them for a better deal this time around. And that doesn't just mean money. It means other factors that authors sometimes want to control/influence, from release dates to covers, etc.
Nora Roberts stopped writing new material for Silhouette because they wouldn't stop releasing her old stuff the same month as she had a new release coming out from another publisher. (Which thereby confused her fans and lead to a canniblizing of the sales of the new work.)
Silhoutte kept the rights to her earlier work by keeping them in print. Now, had some of those rights reverted to her, she could have sold them to another publisher, and gotten control of release dates, so that the re-release of old material didn't interfere with the release of her new material. (So that also shows that sometimes, no matter who you are, you don't have the clout to get them to do what you want. If Nora couldn't influence this... well...
But if she'd had the rights to the earlier works, other publishers would have listened to her when she said she'd sell them rights to publish the books, but on her terms.)
She solved her problem by coming up with a special logo for the covers of her new books that tell her fans which books are new releases.
The problem NOW is with the definition of "in print." For example, Harlequin now releases all new books as ebooks as well as print books. If the contracts allow for the ebooks to count as "in print" then the rights will never revert back to the author - Harlequin could just offer it for sale as an ebook, never actually push the book, never actually sell many copies, and yet, the author is stuck.
An attorney from the Author's Guild whom I've heard speak to a number of different writing groups recommends that in-print clauses in contracts now have some sort of minimum sales number to define "in print." The book is in print as long as the author is making X dollars in Y amount of time frame.
Susan G.