And.. there were far fewer distractions. Waiting for compiling? Maybe you could play solitaire, but there were fewer 'rabbit holes' to go down because... you likely weren't on a network. Even by mid 90s, you weren't easily 2 seconds away from any distraction you wanted, even if you were 'online'.
But for others, especially being closer to hardware, a good book was necessary. These days, it still might be.