I guess business is business and they want to capture more people to play. Now that they have a lot of age games, it is time to make one free for kids and families with micro-payment as they have nothing to loose but to win more money for a next age project.
Btw, I personally like the cartoonish style and would even like, later, to have a cartoonish patch even for DoF, of course not affecting the gameplay just the look of the game. I like cartoons.