In an interview with Gamasutra:
We have never really been annualizers. [Almost] every time we have worked in any kind of excessively quick time span, it hasn't been something we enjoyed, or thought we were able to express ourselves properly, or make it interesting...
Sequels are an interesting thing when youve got something new to say. And we obviously make plenty of sequels, but we really push ourselves to make sure we are not just doing it as a way of trying to fleece out money and strangle a property in its infancy.
I love you, Dan Houser.