There are many things I feel nostalgic for in that era, but chunky manuals for specific software are at the bottom of that list.

They weren’t like textbooks, which have knowledge that tends to be relevant for decades. You’d get a new set with every software release, making the last 5-20 lbs of manuals obsolete.

You did lose some of the readability of an actual book. Hard-copy manuals were better for that. But for most software manuals, I did more “look up how to do this thing” than reading straight through. And with a pdf on a CD you had much better search capabilities. Before that you’d have to rely on the ToC, the book index and your own notes. For many manuals, the index wasn’t great. Full text search was a definite step up.

Even the good ones, like the 1980s IBM 2-ring binder manuals, which had good indexes, were a pain to deal with and couldn’t functionally match a PDF or text file on a CD for searchability.