We've gone right back to feeding tokens (in-game credits) because now you can distribute the equivalent of an single-game arcade cabinet -- a game that is designed to optimally take in cash at a given rate -- to every mobile device. A good analogue would be to make a beat-em up arcade cabinet that let you start out for nothing, but when you inevitably get KO'd, you have to feed it a few tokens for the privilege of continuing before the 15 second countdown elapses and you have to start from the beginning.