Originally posted by Pi.Gi.:

Small Team they have made millions of dollar on this game why not hire a lot of people ?

Software development is kind of like cooking; doubling the number of chefs is not a good way to increase the rate of production. New coders have to get "up to speed" with the existing (spaghetti) codebase, have their incompatible habits and styles beaten out of them, and made to conform. Also, a lot of the integration process requires interacting with the existing team, meaning they're not getting anything done, either.

Doubling the number of carpenters is a good way to get a house built in two thirds of the initial timeframe... doubling the number of coders is a good way to have a 6-12 month productivity lapse.