laziness, inefficiency, unavailablility of original tapes - it's always been chaos with the major labels, and still sometimes a problem to find the actual material.
It's always been an issue frankly - 90% of the time mastering restrictions had a negative effect on how the original audio had sounded in the studio when it was mixed. Very few LPs sounded anything like the original recordings - yes it sometimes added a certain character, but ultimately this has to be about making great records, rather than great recordings!