This is speculation, but this may be related to resource compression and them trying to get the iTunes download size as small as possible since so many people were on dialup at the time: https://news.ycombinator.com/item?id=26415883
System 7 added that overall capability, and Apple shipped 4 different built-in resource compression algorithms over the years (the last of those added in OS 9), but it was equally possible for third parties to ship their own decompression routine's machine code along with the other resources. I remember iTunes using InstallerVISE, and I know VISE came with its own compression routines.
System 7 added that overall capability, and Apple shipped 4 different built-in resource compression algorithms over the years (the last of those added in OS 9), but it was equally possible for third parties to ship their own decompression routine's machine code along with the other resources. I remember iTunes using InstallerVISE, and I know VISE came with its own compression routines.