At the time, CD writers were not a common thing. Supposedly, CD-RW that could be rewritten debuted in 1997. AOL wouldn't have been giving those out. You paid a premium for them compared to the write-once CD-R, which is what most people I knew who burned CDs at home were using. AOL just sent mass-pressed CD-ROMs.

It would be interesting to know how much waste their CD mailing campaign produced. I think it would be a nice gesture to recognize their accomplishment with a monument: the Steve Case Memorial Landfill.