Consequently, being just as good as Shirley or even better didn't count for all that much. Given a choice, theatre goers would choose Shirley. Writers today have the same challenge with D. Steel. Even if you write just like she does, B. Dalton will put Steel's books out in front of yours. So it goes on back up the line.
Publishers invest their money in the best product they can find.
That means already selling authors are a preferred commodity. Give any editor a choice between two books equally well-written, but one submitted by a published author and the other by an unknown, and the editor will naturally go with M. Published. Back up one more step now. An agent gets two books equally well written, and only has room for one more writer. I'll give you three guesses which author gets the happy nod.