Burning CDs. That’s how I know most people didn’t know how to do it, or want to put in the effort. You had to go buy a stack of CDs, hope your computer supported burning, had to make sure players could support the burned disc (depending on if you made a music disc or data disc, if it was rewritable), and spend the time to burn the disc.
Contrast that to ctrl+c ctrl+v.
There’s more people who can ‘duplicate’ digital files than there were people burning CDs.