The points Michael made are all valid, but I am not satisfied by those explanations. The number of lost berths aboard the idle passenger vessels would have overridden concerns about paint smells, etc. on a maiden voyage of a working new ship. Also, people crossing the ocean in 1912 did not do so on a whim. I suspect most had reasons for making the passage at a particular time. Many of the immigrants in 3rd cabin had "sold out" at home, so were effectively homeless without a ship to board.
So, I really don't find arguments about the newness of the ship compelling. Nor am I comfortable with explanations that people put off their voyages to wait for the coal strike to end.
As a passenger vessel owner/operator, I know for certain that unsold tickets on a completed voyage can never be sold again. White Star Line would never have allowed ticket revenue from idle ships to slip away when it could have been realized by re-booking those passengers aboard the new Titanic. The economics of business argue for a full ship every trip.
So, why was Titanic so empty?
--David G. Brown