At the moment, cannon.js supports planes, boxes and spheres to a small extent. It is not yet stable enough to use with an end-user software though. When the software gets stable, we can expect Angry Birds-like games in 3D!
Also, some of the ports contains logical bugs, and many times this is hard to correct for the developer porting the code.
Another reason (probably the most important one) is that I am very interested in a full understanding of a rigid body physics simulator. I admire physics engine developers. Without them we would not have realistic games at all… And Angry Birds would’t even exist.