Why were Marley’s biblical interpretations not subjected to this level of review until now?

Perhaps because Marley is seen as a rebel and a rock star, and these aspects appear to exist in opposition to the world of the Bible. But the Bible does not exist apart from the world of the rebel. In fact, Marley sings about Paul Bogle and Marcus Garvey, rebellious figures in their own right who were inspired by their reading of scripture. Marley continues in a long line of scriptural resistance.