Games in general, but specifically AAA+ games, have an insanely risky business model. From early concept to release is often 4+ years of heads down development with zero revenue. Tastes and trends change within that time and what may have been a compelling concept 4 years ago might seem stale by release. Then there is balancing the game which is a monumental challenge in itself; when you've been playing the same game for several years you lose perspective on what's fun or not, what is easy/difficult, etc.
