Problem is how to handle worst-case scenarios. With pre-rendered movies that might or might not be a problem, and even if it is - it's production one (e.g. you can't predict how many well for how many days you would render your movie) But for a game - this means dropping the frame rate, making it visually unappealing. That's why Ray-casting would never pick up for real-time games (Unreal most definitely is not doing…
I'm not convinced that you are correct here. Although ray-tracing has not been a good option in the past due to processor limitations, we're reaching the point at which it may become feasible. Because ray-tracing scales linearly with the number of cores you use, modern CPUs are fairly well equipped to work with it, albeit at sub-optimal framerates. See the following (from 2007) for reference: http://www.q4rt.de/
Outside of this, consider that the only way vector graphics are allowed to perform at their current level is due to the existence of discrete graphics cards which are optimized for the necessary matrix calculations. If we were to develop discrete cards for ray-tracing, we could potentially see amazing results. For example, in 2009 IBM developed a computer that could run full-scene ray-tracing at 1080p averaging 90 FPS. While I do not know how complex said scene was, I'm optimistic about the future of ray-tracing.