Do we know that it can actually predict the future? Evidently Orolin didn't read the future in it. Neither did Rayek. If Timmain ever did, she's keeping quiet about it. Rayek and Cutter were worried about Winnowill getting that power during the "Shards" quest, but evidently no one ever reads the future in it. Or ... perhaps the scroll itself is intelligent, and doesn't allow that sort of access, even if it is possible. That seems to make a lot of sense to me; everyone who has had contact with the scroll believes that reading the future is possible, but no one ever does; perhaps the elves are being manipulated.