This is such an interesting question and I've thought about this a lot with good writers. What I see in Carver and Chekhov, and others, is that there is a lot of information packed into a small amount of space. There is also a lot happening. It might not be a car chase, but it is thoughts, emotional or mental movement, changes inside and out. These good writers also know a lot about people. It is like looking inside and seeing secrets.

In contrast, look at your typical potboiler. In chapter one there is the hero. S/he might have a flaw, its the same flaw. It's a stereotype. They are trying to do something. 10 chapters later, they are trying to do the same thing. If you put the book down in the middle, two days later you can barely remember what it was about.

In contrast, a great book can be picked up years later and restarted. You can remember the outlines after skimming a few pages here and there. At the end, you have something to think about.