That's because his book was all about "routines". That's selection bias right there.
If you read random artist biographies you're rarely gonna find the same emphasis on routines.
In science, major breakthroughs don't usually come from strained application of rational thinking, they come from spontaneous intuitive leaps. These leaps occur more readily when the mind is in a relaxed state free from worry and distractions, where you can just let your thoughts wander.
And that relaxed state comes from externalizing your process into structure and routine, so your mind can focus on high thinking and not juggling all your cluttered concerns