This is not a technical problem at all. This is a copyright problem. Anthropic thought it was just a technical problem until they had to pay 1.5 billion after they lost a copyright court case

Op means a lot of those books were made before computers were used for that purpose and the publishers and probably authors no longer exist, so there is no digital copy to just reprint, unless someone scans it themselves and publishes it, risking copyright violation when done at large scale due to possible exceptions to this rule