CD Bler on very old media



I was curious and wanted to check the quality of my oldest media.
While testing I realised that for none of the media which were burnt before 1998 I was able to do an advanced scan (eg CD Bler with ODC)

Even for CDs in pretty good shape like it stopped after some second scanning.

What is the reason for it? Is this a general problem (different dye), does it depend on the reader or is it only a coincidence?