This is a bit random, but do publishers like Penguin move a lot of classics each year? Middlemarch’s rank in the Amazon USA list would seem to indicate it sells around ten copies a day. Does that seem reasonable? I thought it seemed a bit low, but my opinion is truly random. There are >12 different paperback editions, so that would seem to argue for popularity…
It’s maybe worth noting that Penguin Classics and other similar publishers release a lot of new translations of works, as well as often providing in depth introductions and notes in their books, so you’re not just getting the same stuff you’d get in a public domain version. This stuff is great for people who want to read them more than casually, but not to the extent of fully studying the works and getting multiple books about them.
The Iliad has been riding high in new book sale lists over the last few weeks specifically because Emily Wilson’s new translation carried a lot of hype. Kind of cool to see.