Ray Tracing versus object-based rendering?
Raytracing is a very nice and intuitive algorithm, and it is a more physically realistic way of describing the illumination of a scene than rasterization, but:


Raytracing is slow, specially if you want to implement the more realistic effects that distinguish it from rasterization (e.g. refraction, reflection, motion blur, soft shadows) because this implies creating a lot more rays per pixel. 
Most people can't tell the difference between real and fake effects, which I think is the key point. The goal of a practical rendering algorithm is to create a photorealistic representation of a scene in the most efficient way, and right now Rasterization, although uses a lot of hacks, accomplishes this very well. 
There are many other practical limitations of Raytracing compared to a Rasterization renderer: poor anti-aliasing and displacement mapping, limited instancing, etc.


Even in non-interactive applications, such as movies, Raytracing is used very little becasue of its limitations. Pixar only started using Raytracing in Cars, and only for some specific reflection effects (Ray Tracing for the Movie ‘Cars’).

Here is an excellent article that describes in more detail the current state of Raytracing and its advantages and disadvantages: State of Ray Tracing (in games).