The Commodore 64 has a cartridge slot, but by the mid-eighties, cartridge games disappeared; everything was on tape or disk. Why?
One answer that suggests itself is that by that time, a larger percentage of owners had disk drives. However, that was less true in Europe, and in America, if you ask why Nintendo replaced Commodore, one of the reasons usually given is the speed and convenience of cartridges over the slow and clunky 1541 disk drive, so why was there not a preference for the speed and convenience of cartridges on the 64?
It's true that cartridges cost more per unit to produce, but they also eliminate piracy; would this not offset the increased cost, from the vendor's viewpoint?