They are choosing a house that can have a sustainable run. At about 1000 seats as opposed to the 1600+ at both the St. James (Rotten!) and the Marquis(Tootsie!), they have set themselves up to be a high-priced, sold-out hit show at the intimate Sondheim, as opposed to struggling to fill 600 additional seats by going to a bigger theatre. If Tootsie had been at a smaller house, Its numbers would look a little better than how it is showing at the Marquis.