Just because they kept it doesn't mean they read it :).
After all, the Israelites kept it too, yet in King Josiah's day the Pentateuch had gone unread for countless generations (2 Kings 22:8-11) until the day King Josaih obeyed God (Deuteronomy 31:9-13) and read it aloud before all of Israel (2 Kings 23:1-3).
It's like saying just because some Martian shows up with a long lost copy of the Declaration of Independence we should make him President.