One reason they stopped doing that was because it made it too easy to make clones (https://en.wikipedia.org/wiki/Apple_II_clones https://en.wikipedia.org/wiki/A

One reason they stopped doing that was because it made it too easy to make clones (https://en.wikipedia.org/wiki/Apple_II_clones https://en.wikipedia.org/wiki/Apple_II_clones) It was Apple Computer, Inc. v. Franklin Computer Corp. (https://en.wikipedia.org/wiki/Apple_Computer,_Inc._v._Franklin_Computer_Corp https://en.wikipedia.org/wiki/Apple_Computer,_Inc._v._Frankl....) that led to the judgment that software stored in ROM was copyrightable in the US, requiring Phoenix Technologies to make a clean-room implementation of the BIOS of the IBM PC (https://en.wikipedia.org/wiki/Phoenix_Technologies#Cloning_the_IBM_PC_BIOS https://en.wikipedia.org/wiki/Phoenix_Technologies#Cloning_t...)