The reason is it's a hell of a lot cheaper and easier to work with, and in general enables things to be done that would otherwise be cost prohibitive. (And AFA

The reason is it's a hell of a lot cheaper and easier to work with, and in general enables things to be done that would otherwise be cost prohibitive. (And AFAIK they do usually do a non-realtime run, but a high-end render going for maximum photorealism also requires a whole different pipeline for modelling and rendering, which would essentially blow the budget even more so)