I worked at a university bookstore and we sold lots of disks. while CDs were killing them for long-term storage zips were required for some courses because RW disks suck.

those zip disks were not cheap 10$-15$ each for a paltry 100mb.

the rise of USB sticks really killed them. you could get a 128mb usb stick for similar or cheaper and you didn't need the clunky unreliable zip drive to use them.