Pixar have a lot of technology, but they come from an animation tradition rather than a studio that is concerned with photoreal CGI. Renderman has always been a system for "painting" the scene you want - it's an artist's toolbox.
It's only recently that advances in processing power have made physically-based ray tracing practical for film production - particularly with the take-up of the Arnold renderer by various other studios. Suddenly lighting becomes a matter of placing lights and letting the computer do the work rather than needing to carefully set up the correct impression of light in the way a painter might. So it requires quite a bit of change of approach from the artist, and you can imagine why there'd be a bit of a cultural problem introducing this.
It's only recently that advances in processing power have made physically-based ray tracing practical for film production - particularly with the take-up of the Arnold renderer by various other studios. Suddenly lighting becomes a matter of placing lights and letting the computer do the work rather than needing to carefully set up the correct impression of light in the way a painter might. So it requires quite a bit of change of approach from the artist, and you can imagine why there'd be a bit of a cultural problem introducing this.