Im not even concerned about the hardware failure or disc rot. My big issue has always been a disc can look mostly fine but that one little micro-scratch can make the game freeze and crash during the last sequence of the game. Never letting you finish it, and unless you played the game to that point you would never know.
Or you have some disc that were used as hockey pucks that, by some miracle, work perfectly fine. But I would never buy them because of how they look.
Too much of a guessing game. At least with carts, if it fires up you know it’s good all the way through.