I loved this range of classics that Barnes and Noble used to have. They were all about six by four inches and five dollars each. Hardcover, gold-edged, and clothbound, too. Perfect for me because they didn't have pictures on the cover (I don't know why that often bothers me) and were small enough to fit in a purse. I was only able to get eight before they stopped making them a couple years ago.
Now they still have good-priced classics, in hardcover and paperback, but they're just not the same. They're bigger. I don't like books to be big. Though the pages do have a little more space for scribbling. I tend to do some informal annotating on the classics to make sure I'm not missing things. So I guess that's nice, but still.
To answer my question, though, I think it's because most people aren't like me. They don't want small books. The old ones were tiny. Most people would probably pass them by, thinking they were abridged or something.