How did David Bowie transition from genre to genre so easily?

Good question. Not a lot. A great example is Led Zeppelin, who were known primarily as Blues-Rock, but they were known for being Heavy Metal (Kashmir), Progressive rock (Black Dog), Country Rock (Bron-Y-Aur Stomp), Celtic Folk/Folk Rock (First half of Stairway to Heaven), Rock and Roll (other half of Stairway to Heaven), Blues (Since I've Been Loving You), Caribbean (D'yer Mak'er), Funk Rock (Trampled under Foot), the list goes on. Mainly because they dipped into many styles.