It may well be true that most people don't re-read their books. My experience is that
- I can't afford to buy enough books to keep myself in all-new reading material
- My public library doesn't have enough of what interests me to fill the gap
- Most of what I can borrow from friends is books I have already read
So I wind up re-reading.
As with nearly everything, your mileage will almost certainly vary.
Xenophon