This isn't quite true. There have been 5-10 codices recovered from tombs, but none of them are preserved well enough to be read. In a couple of cases there are clumps of pages that we hope to be able to read bits of in the future, but they're too brittle and fragmentary to be opened and read. As far as I know, there's been no progress on any of them, but archaeology usually borrows technological advances from other disciplines, so the breakthrough is likely to come from somewhere else and then applied by archaeologists to read some of these fragmentary codices.