The **fixed cost** of an optical drive is of course much higher than the fixed cost of a USB port.
However, the **variable cost** of optical disks is much lower than the cost of thumb drives.
(EDIT: **At high volumes**, it is much cheaper to “press” the data onto disks at a factory, like how movies are currently put on DVDs.) If optical disk burners did not exist, then it would be cheaper to sell **low-volume** games on thumb drives. But optical burners **do** exist, so it’s almost as cheap to burn disks and then mail them out.
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