No, it's that I don't buy used books. Libraries pay for their books and they introduce people to authors they might pay money for later. There is no author on earth who thinks library sales are a bad thing.
But used books, now that they are so easy to get, are a different kettle of giraffe. It was one thing when you'd maybe stumble across something in a used book store that you'd never have otherwise thought to read, and then go buy more stuff by the author because it could take years to stumble across another of their books. Now you can go to the Amazon listing looking for a specific book and with the same one-click, buy a used book instead of one that will count as a sale for the author. And then easily buy all their other books the same way. My last book had cheap used copies for sale on its Amazon listing basically immediately. And the reason I haven't gotten to publish another book since then is not unrelated to that fact that that book didn't sell enough NEW copies.