You are confusing the "norm" at the time, with Apple specific decision to open up their hardware. At the time, a lot of consumer electronics shipped with their schematics, including TVs, Radios, etc. You cannot find a single TV today that ships with how to talk over its diagnostics port let alone schematics.

The Apple computer you're referencing was more like an of IC of today, both in complexity (many $1 ICs today are orders of magnitude more complex than that entire computer), and the skills expected of the user of the computer. Both of which would require one to have intimate knowledge of the inner working of the device to be able to operate and maintain it. Users of that computer were like hobbyist of today, buying an electronics kit and rest assured, electronics kits come with detailed manuals, schematics and more.