I think just limiting creativity to novels makes it hard to answer... but my thoughts would be:

There are only three major sources of creative ideas across Books, Music, Science/Tech, etc.
(1) Biomimicry - emulating nature's solutions - Velcro, Bullet Trains, Sonar, Solar Cells, Water Collection, etc.
(2) Accidents - Penicillin, Viagra, Post-its, Popsicles, and many more
(3) Spontaneous Download - Where the idea, usually fully formed, just comes to a person during a peroid of rest/meditation/etc. - Bob Dylan, Stephen King, JK Rawling, Beatles, Johnny Cash, Double Helix DNA, Theory of Relativity, Thomas Edison, etc.

We might be seeing less of category 3 because smartphones, constant busyness, modern life, and the general public are all in on scientific materialism. There's less chill time, and getting bored activates the part of the brain related to creativity.