delericho
Legend
Where does this 1 bigger book is more profitable than 2 smaller ones comes from? If those two smaller books are more popular than the one then the two are clearly better.
Because while it costs more to produce a 200 page book than a 100 page one, it costs less than twice as much. Because they get a greater margin on each copy sold of a larger book than a smaller one. Because they know that sales drop off the further you get into a series (that is, sales of "Rise of Tiamat" were never going to equal those of "Hoard of the Dragon Queen"). And because a customer being offered 2 100-page books at $30 each may well feel ripped off, while one being offered a 200-page book for $40 is less likely to.
There isn't a single, simple reason why the bigger book is better. But there's a reason that the trend has very much been towards larger, full-colour, hardback books. Unfortunately, while dropping each of these things will reduce the end cost, it's only by a little each time.
(As for why Paizo are able to produce monthly 100-page Pathfinder AP volumes for $23 each time where WotC cannot, one word: subscriptions.)