I think both Alphax and Jon Stanard made good points.
First, how many people really need that kind of massive storage on a removable disk. This the exception of a few games, nothing I’ve looked at software wise needed more than 1 CD worth of information. People who need more storage than that typically use DVDs.
Second, current writing technology is pushing the data transfer rates on many home machines. I’m not 100% sure that this is an issue for Macs, but ask any techie who has worked with PCs if they get much more than 16x out of a CD burner, and they will tell you no, because it is buffer underrunning too often. This is not a limit of CD technology, but the fact that you rarely see drives mose faster than 50x is. The discs can’t take it. Eventually, how much data you can fit into the same area will hit its limit as well. Eventually a more efficient design than optical disks must be found.