We've been in the game since the beginning so I've seen the transition from selling a game at $4.99, then $2.99, then $0.99, and finally free with IAP. Despite being very successful we didn't enjoy that trend, but instead just adapted to it.
It's purely a response to the mobile consumer's spending habits and their complete unwillingness to psychologically accept the "risk" that the $5 or $2 game they bought might not be as fun as they hoped.