There are multiple reasons here.
Simply put, cartoony graphics are considerably cheaper to develop than the high realism 3D cinematics.
Animated cartoons don't have the biggest audience (compared to live action movies). The smaller the profits, the smaller the development budget.
Without having seen the numbers (I can't find any reasonably ...
The answer will have to be "it depends". It's got to depend on the director, the casting director, possible changes to the script, etc.
An interesting case regarding script changes: One draft of the script for Close Encounters of the Third Kind included a topless scene with Teri Garr. However, that scene was never shot, and the actress never had to appear ...