Because all novelists hire their pens in advance for years, and have no time left for outside labour.
And last, and (perhaps) not least, Why don't I send in a play? Because I have tried to write one, and find I can't quite manage it!
Her First Play.
Mamma (who has taken Miss Effie, as a great treat, to a morning performance). "Hush, dear! You mustn't talk!"
Miss Effie (with clear sense of injustice, and pointing to the stage). "But, mummy,—they're talking!"