Because even if you have an edge at a game of skill and chance, it's not a license to print money. Professional blackjack players have to fly under the radar,

Because even if you have an edge at a game of skill and chance, it's not a license to print money. Professional blackjack players have to fly under the radar, and even with the large bankroll needed to survive swings, can only expect to make somewhere in the 5 figures. Plus, you have to spend all your time playing blackjack. Wouldn't you rather sell a book?