Both require very specific skill sets as clients want to see what a model or actor can do.
Models must move effortlessly in front of the camera; they have to know their angles and facial expressions. They need to be able to walk and have confidence. Audition techniques are things that a model must know. In today's world, models also need basic on-camera skills.
Actors must have a range of skills. From improv, cold reading techniques, on-camera skills, and how to read scripts and storyboards.
The bottom line is that in today’s world, models and actors have to have skills, and it is not an agency's job to fund that experience.