I've wondered about whether modern computers should come with the comprehensive manuals of the era. The Raspberry Pi 400 attempted to do it. But the problem isn't as much that companies don't want to ship these big manuals, but it's that 1) Nobody would read them because of the Internet and, most importantly, 2) you can't create comprehensive documentation of a modern computer in a reasonably sized book.

The biggest change from the good old days is that one could truly hope to fully understand a machine. The C64 was a bit harder, but not impossible. But the Speccy was simple enough that a near-100% understanding was achievable. This feeling of full control is what we lost.