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…
I think some people have a favourite classic and will buy a few copies of it or are gifted them if they are particularly nice e.g. Macmillan collectors’ library editions. I have three different editions of Persuasion.