Making a simple scene requires the making of models and background or environment. The environment has to be made separately. A model requires the actual 3d models geometry, rigging (in order for the geometry to move), textures to give the model a surface, and an animator which blocks the movement frame by frame. Then you’d also need someone exclusively animating the camera, and depending on the production pipeline a different process of making special effects and shaders to treat the illumination and materials. Some of these parts can be made by the same person but usually, specially in high quality productions, a different highly trained specialist will handle each part separately. Each is an art form that requires lots of education, skills and hours of labor to make.
For instance, the most recent spider man animated film, Across the Spider-Verse, took roughly 5 years to produce. For contrast, Snow White, the first animated film took roughly 4 years to make. Just because something is computer animated doesn’t mean it was easier or took less time to make. Most computer animators receive training in classical 2d animation, as most basic skills and principles are transferrable. Also, most 3d animated films today include a lot of digital 2d work to achieve the artists desired vision.