Kendrick is out here training on the moon, Goku style. Stacking paper on the road, improving his show, and spending his time well in the studios. A lot of rappers just record a bunch of songs in the studio that never come out, or are released on mixtapes/iTunes bonus. Kendrick actually records demos. He saves beats. He experiments with multiple flows on tracks, etc. I bet he barely has any finished songs for his new album. But when it's time to record, when he finally figures out what he wants to say and do next, he'll have a laptop full of melodies, beats, fragments, etc to choose from.
I bet producers love working with him. Imagine the horror in Just Blaze's face when he realized Ross was wasting this classic beat with throwaway rhymes, brehs...
Kendrick would have kept that beat for months, playing around with it before deciding how to tackle it, and coming up with a decent hook.