Does every republished book have an audience?

Don't get me wrong: I really enjoyed Lizzie Skurnick's Shelf Discovery. But here's an article from Jezebel saying that Skurnick has arranged to have some of the obscure titles from Shelf Discovery (and at least one, Lois Duncan's Debutante Hill, that doesn't appear in Skurnick's book) republished.
I can't work this out. Why bother? Isn't this what inter-library loan and abebooks.com are for? I think that there's certainly a place for old books being republished: there are some lovely new editions of Dorothy L. Sayers's mysteries, and I have bought quite a few books from Image Cascade and Girls Gone By Publishers. But those two publishers specialize in hard-to-find titles, and sell most of their books to collectors of old children's books. But will there be a market for old books from the 1970s and 1980s?